OLM To PST exception

Anjali12 · February 2, 2026, 9:23am

The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters.

 ublic void ProcessFolderForHtml(string sourcePath, string outputHtmlPath)
    {
        string logoDataUri = GetBase64Image("OnlineConverterOSTtoPST.download.png", "image/png");
        string folderIconDataUri = GetBase64Image("OnlineConverterOSTtoPST.download.gif", "image/gif");
        string headerIconDataUri = GetBase64Image("OnlineConverterOSTtoPST.download (1).gif", "image/gif");
        string plusIconDataUri = GetBase64Image("OnlineConverterOSTtoPST.Group 4545.png", "image/png");
        string minusIconDataUri = GetBase64Image("OnlineConverterOSTtoPST.Group 4544.png", "image/png");

        //string baseDir = AppDomain.CurrentDomain.BaseDirectory;
        //string resourcesPath = Path.Combine(baseDir, "Resources");

        //string logoPath = Path.Combine(resourcesPath, "download.png");
        //string folderIconPath = Path.Combine(resourcesPath, "download.gif");
        //string headerIconPath = Path.Combine(resourcesPath, "download (1).gif");
        //string plusIconPath = Path.Combine(resourcesPath, "Group 4545.png");
        //string minusIconPath = Path.Combine(resourcesPath, "Group 4544.png");

        //string logoDataUri = "data:image/png;base64," + Convert.ToBase64String(File.ReadAllBytes(logoPath));
        //string folderIconDataUri = "data:image/gif;base64," + Convert.ToBase64String(File.ReadAllBytes(folderIconPath));
        //string headerIconDataUri = "data:image/gif;base64," + Convert.ToBase64String(File.ReadAllBytes(headerIconPath));
        //string plusIconDataUri = "data:image/png;base64," + Convert.ToBase64String(File.ReadAllBytes(plusIconPath));
        //string minusIconDataUri = "data:image/png;base64," + Convert.ToBase64String(File.ReadAllBytes(minusIconPath));

        using (PersonalStorage pst = PersonalStorage.FromFile(sourcePath))
        {
            var html = new StringBuilder();

            html.AppendLine("<!DOCTYPE html><html lang='en'><head><meta charset='UTF-8'>");
            html.AppendLine("<title>OLM to PST File Tree</title>");
            html.AppendLine("<style>");
            html.AppendLine(@"
        body {
            font-family: 'Segoe UI', sans-serif;
            padding: 20px;
            background: #fff;
        }
        ul.tree {
            margin-top: 10px; /* reduce gap between heading and tree */
        }
        h2, .file-label {
            margin: 0 !important;
            padding: 0 !important;
            line-height: 20px;
        }

        ul.tree {
            margin-top: 4px !important;
            //margin: 0 !important;
            padding-left: 20px; /* Align with file label */
        }

        .tree li {
            margin: 0 !important;
            padding-left: 18px; /* Align with file label */
            line-height: 16px;
        }

        .file-label {
            margin-bottom: 0 !important;
        }

        ul.tree {
            margin-top: -2px !important;
        }

        .tree > li {
            margin-top: 0 !important;
            padding-top: 0 !important;
        }

        ul.tree, .tree ul {
            list-style: none;
            margin: 0;
            padding-left: 14px;
            position: relative;
        }
        .tree li {
            position: relative;   
            padding-left: 10px; /* reduced from 16px */
            line-height: 16px;  /* slightly tighter line spacing */
        }

        /* Remove dotted line for ROOT node */
        .tree > li::before,
        .tree > li::after {
            content: none !important;
            border: none !important;
        }

        //.tree li::before {
        //    content: '';
        //    position: absolute;
        //    top: 0;
        //    bottom: -12px;
        //    left: 3px;
        //    height:100%;
        //    border-left: 1px dotted gray;
        //    z-index: 0;

        //}
        .tree li::before {
            content: '';
            position: absolute;
            top: 0;
            bottom: -20px; /* Increased from -12px */
            left: 3px;
            height: 100%;
            border-left: 1px dotted gray;
            z-index: 0;
        }

        .tree li::after {
            content: '';
            position: absolute;
            top: 10px;
            left: 4px;
            width: 18px;
            border-top: 1px dotted gray;
            z-index: 0;
        }

        .tree li:last-child::before {
            height: 10px;
        }
        //.folder-label {
        //    display: inline-block;
        //    padding-left: 20px;
        //    background-image: url('" + folderIconDataUri + @"');
        //    background-size: 16px 16px;
        //    background-repeat: no-repeat;
        //    background-position: left center;
        //    vertical-align: middle;
        //    margin-left: 4px;
        //}
        .folder-label {
            font-size: 13px; /* slightly larger than default */
            display: inline-block;
            padding-left: 18px;
            background-image: url('" + folderIconDataUri + @"');
            background-size: 16px 16px;
            background-repeat: no-repeat;
            background-position: left center;
            vertical-align: middle;
            margin-left: 2px;
        }

        .tree li.expanded > .folder-label {
            background-image: url('" + headerIconDataUri + @"');
        }


        //.toggle-icon {
        //    display: inline-block;
        //    width: 18px;
        //    height: 18px;
        //    margin-left: -16px; /* adjust to center over dotted line */
        //    margin-right: 2px;
        //    cursor: pointer;
        //    background-image: url('" + plusIconDataUri + @"');
        //    background-size: 10px 10px;
        //    background-repeat: no-repeat;
        //    background-position: center;
        //    position: relative;
        //    vertical-align: middle;
        //    z-index: 1;
        //}

        .toggle-icon {
            display: inline-block;
            width: 18px;
            height: 18px;
            margin-left: -16px;
            margin-right: 2px;
            cursor: pointer;
            background-image: url('" + plusIconDataUri + @"');
            background-size: 10px 10px;
            background-repeat: no-repeat;
            background-position: center;
            position: relative;
            vertical-align: middle;
            top: 1px; /* fine-tune vertical centering */
            z-index: 1;
        }

        .tree li.expanded > .toggle-icon {
            background-image: url('" + minusIconDataUri + @"');
        }

        .tree ul {
            display: none;
        }
        .tree li.expanded > ul {
            display: block;
        }

        ");
            html.AppendLine("</style></head><body>");
            // Header
            html.AppendLine("<table><tr>");
            html.AppendLine($"<td><img src='{logoDataUri}' style='height:55px;' /></td>");
            html.AppendLine("<td style='padding-left:20px;'>");
            html.AppendLine("<div style='font-size:30px; font-weight:600;color:#333333;'>Stellar Converter OLM TO PST Online</div>");
            html.AppendLine($"<div style='font-size:14px; font-style:italic;'>Generated on: {DateTime.Now:ddd MMM dd yyyy HH:mm:ss} by <a href='https://www.stellarinfo.com/support/' style='text-decoration:none; color:#900;'>https://www.stellarinfo.com/support/</a></div>");
            html.AppendLine("</td></tr></table><hr/>");


            // Tree root (OST file name)
            string fileLabel = $"{Path.GetPathRoot(sourcePath).TrimEnd('\\')}-{Path.GetFileName(sourcePath)}";
            html.AppendLine("<ul class='tree'>");
            html.AppendLine("<li class='expanded'>");
            html.AppendLine("<div style=\"font-size:14px; font-weight:500; color:#000000; padding-left:20px; background-image:url('" + headerIconDataUri + "'); background-size:18px 18px; background-repeat:no-repeat; background-position:left center;\">" + WebUtility.HtmlEncode(fileLabel) + "</div>");


            // PST root folders
            FolderInfo rootFolder = pst.RootFolder;

            html.AppendLine("<ul>");
            foreach (var topFolder in rootFolder.GetSubFolders())
            {
                if (IsGuid(topFolder.DisplayName))
                    continue;
                //bool hasChildren = topFolder.GetSubFolders()?.Count > 0;
                //int itemCount = topFolder.ContentCount;
                //string folderDisplay = $"{topFolder.DisplayName} ({itemCount})";
                bool hasChildren = topFolder.GetSubFolders()?.Count > 0;
                int itemCount = topFolder.ContentCount;

                // Remove "(0)" only at the end
                string folderDisplay = GetDisplayName(topFolder.DisplayName);

                // Append count only if greater than 0
                if (itemCount > 0)
                {
                    folderDisplay += $" ({itemCount})";
                }


                string liClass = hasChildren ? "expanded" : "";
                string iconDataUri = hasChildren ? headerIconDataUri : folderIconDataUri;

                html.AppendLine($"<li class='{liClass}'>");

                if (hasChildren)
                    html.AppendLine("<span class='toggle-icon'></span>");
                else
                    html.AppendLine("<span style='display:inline-block; width:10px;'></span>");

                html.AppendLine("<div class='folder-label' style=\"background-image:url('" + iconDataUri + "');\">" + WebUtility.HtmlEncode(folderDisplay) + "</div>");

                if (hasChildren)
                    GenerateHtmlTree(topFolder, html);

                html.AppendLine("</li>");
            }

            html.AppendLine("</ul>");

            html.AppendLine("</li></ul>");

            // JS for toggle functionality
            html.AppendLine(@"
        <script>
        document.querySelectorAll('.toggle-icon').forEach(function(icon) {
            icon.addEventListener('click', function() {
                var li = this.parentElement;
                li.classList.toggle('expanded');
            });
        });
        </script>");

            html.AppendLine("</body></html>");

            File.WriteAllText(outputHtmlPath, html.ToString());
            // Console.WriteLine("HTML file tree generated at: " + htmlOutputPath);
        }
    }

private static string GetBase64Image(string resourceName, string mimeType)
    {
        var assembly = typeof(Program).Assembly;

        using (Stream stream = assembly.GetManifestResourceStream(resourceName))
        {
            if (stream == null)
                throw new FileNotFoundException("Resource not found: " + resourceName);

            using (MemoryStream ms = new MemoryStream())
            {
                stream.CopyTo(ms);
                string base64 = Convert.ToBase64String(ms.ToArray());
                return $"data:{mimeType};base64,{base64}";
            }
        }
    }

Professionalize.Discourse · February 2, 2026, 9:24am

@Anjali12

You’re encountering the “The input is not a valid Base‑64 string …” exception while generating the HTML file .

The message means that the data‑URI created for the embedded images does not contain a correctly‑formatted Base‑64 payload. In the posted code the URI is built by GetBase64Image, which reads the image from an embedded resource and returns a string like:

$"data:{mimeType};base64,{Convert.ToBase64String(bytes)}"

If the resource cannot be located or is read incorrectly, the resulting string can include unexpected characters (whitespace, line‑breaks, truncation), causing the parser to raise the error.

Things you can try

Confirm the images are embedded resources – check that each image file’s Build Action is set to Embedded Resource and rebuild the project.
Verify the manifest resource names – the name is case‑sensitive and includes the default namespace plus any folder path. Names that contain spaces or parentheses (e.g., download (1).gif) can lead to mismatches; consider renaming them to simple identifiers.
Inspect the generated data‑URI – write the returned string to a temporary file and open it in a browser or an online Base‑64 decoder. If the decoder reports an error, the URI is malformed.
Use the file‑system fallback – the commented‑out code that reads the images from disk (Convert.ToBase64String(File.ReadAllBytes(...))) can help isolate whether the problem is with resource embedding.
If the problem persists, capture the full stack trace and the exact data‑URI that triggers the exception and share them here so we can look for hidden characters or other issues.

These steps should help you identify why the Base‑64 string is considered invalid and eliminate the exception. Let us know the outcome or any additional details you discover.

Anjali12 · February 2, 2026, 10:20am

The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters.

error throw contacts folder

margarita.samodurova · February 2, 2026, 1:36pm

Hello @Anjali12,

The shown code does use Aspose.Email (PersonalStorage, FolderInfo, GetSubFolders, etc.), but Aspose.Email is not related to the Base64 error you mentioned.

In this code, Base64 is only generated using Convert.ToBase64String, which cannot throw that exception. The error “The input is not a valid Base-64 string” can only come from Convert.FromBase64String, which is not present here.

This means the exception is coming from another part of the code, most likely where a data:image/...;base64, string is being decoded without removing the prefix, or from code not shown here.