Attachments arriving as empty Zip file

When a user sends a form with an attachment, even if it comes as document, which opened it is a zip file with no document to be found.

This problem only seems to happen in Microsoft Outlook.

This sounds like an issue with your Outlook settings. Here's a similar thread on the Outlook support forums.
http://social.technet.microsoft.com/Forums/en-US/officeitpro/thread/8c0f4d06-d4cf-43d0-9fc3-3f342c54e966/

Topic closed.