My SharePointBuddy (SPB) recently ran into an issue on an InfoPath form she was working on. Someone went in to try and update the form, and they received the following error:
This wasn’t a form we wanted to recreate from scratch, yet most attempts to fix it weren’t giving the results we needed.
SPB finally found the answer located at http://social.msdn.microsoft.com/Forums/sharepoint/en-US/f0555e7c-5ba0-40bc-82b8-89b2899f20a6/cannot-open-info-path-file-from-sharepoint
She had the customer take the following steps:
- Go to C:\users\username\Appdata\local\Microsoft\
- Create a backup of the folder “InfoPath” then delete the contents of the original “InfoPath” folder.
- Next, go to C:\users\username\Appdata\Roaming\Microsoft\
- Create a backup of the “InfoPath” folder and then delete the contents of the original “InfoPath” folder
Voilà! The problem was fixed and everyone was happy.
SharePoint Duffbert 
This did not fix the problem for me. Any other suggestions?
Unfortunately, no… in fact, we haven’t seen this error in some time.
I believe there is a built-in way to do what you just explained:
1. Hit Windows-R
2. Type: Infopath /cache clearall
3. Hit enter
This should clear your infopath cache
Cool… I did not know that.