Invalid length for a Base-64 char array

I'm trying to use the Sharepoint 2003 Multiple Documents Event Template.
But I wanted to know what option to choose amongst:

1) Sharepoint Attachment Field or the 2) XML Document that contains Attachments.


I chose XML Document that contains attachments option and chose the Upload option to upload the processed InfoPath form into a SharePoint document library. But here, I get an error which states:
"Invalid length for a Base-64 char array."

I need to upload the latest version of the document to this SharePoint document library, but not able to. How do I solve this problem?