Adobe 11 - there was an error opening this document. The file is damaged and could not be repaired.

I'm getting the above error on many files sent to us by customers.

I've tried the reg hacks.

I've updated to v.11.0.23

I've tried unchecking the enhanced security check box.

Here's the interesting thing -

When the user receives the PDF in email and gets the error message, if the user clicks forward to forward the email with the attached PDF, now the PDF can be opened.

I'm stuck on this one.