iTextSharp: Adobe reader could not open xxx.pdf because it is either not a supported file type.

I am using the code from:

http://www.aspsnippets.com/Articles/Export-ASPNet-Web-Page-with-images-to-PDF-using-ITextsharp.aspx

Everything seems to work, expect when I try to open the PDF file Adobe Reader says:

"Adobe reader could not open 'filename.pdf' because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded)."

Any ideas?  I tried opening it in Adobe Photoshop and was not able to there either.