Thank you for contacting Aspose support.
We have evaluated your presented scenario against the latest version of Aspose.Cells for .NET (Latest Version)
, and we are unable to observe any exception while converting your provided sample to PDF format. Please check the following code & the attachment for the resultant PDF file.
In case you are using any older revision of the API, please give a try to the latest version. If you are already using the latest version then you must be performing other operations on your sample before converting it to PDF, in this case, please share your complete code (most preferably a standalone executable sample application).