Again, I've got people downloading the same form from the same place - some submit, some don't. Nobody has made changes to the form in the meantime. This is very mysterious and super annoying.
PDF submit requires Adobe Reader/Acrobat Pro in order to work.
Please see the following articles covering this:
http://forums.adobe.com/docs/DOC-2653
http://forums.adobe.com/docs/DOC-4142
-Jeff Canepa
I was emailed the files and couldn't submit them either. As well, those same people have had no trouble submitting many FC forms over the last few months.