Hi,
I think it might be Https / SSL problem. Could you try to replace the Workbook.Save() line of code by the following code to make sure if it work fine for your need.
[C#]
//Saves file to memory
MemoryStream stream = new MemoryStream();
excel.Save(stream, FileFormatType.Default);
response.ContentType = "application/vnd.ms-excel";
//This is same as OpenInExcel option
response.AddHeader( "content-disposition","attachment; filename=book1.xls");
//This is same as OpenInBrowser option
//response.AddHeader( "content-disposition","inline; filename=book1.xls");
response.BinaryWrite(stream.ToArray());
[Visual Basic]
'Saves file to memory
Dim stream As MemoryStream = New MemoryStream()
excel.Save(stream, FileFormatType.Default)
response.ContentType = "application/vnd.ms-excel"
'This is same as OpenInExcel option
response.AddHeader("content-disposition","attachment; filename=book1.xls")
'This is same as OpenInBrowser option
'response.AddHeader( "content-disposition","inline; filename=book1.xls")
response.BinaryWrite(stream.ToArray())
Thank you.