I ran into a case today where a user was not able to open an attachment. It kept giving the error "cannot create [filename]" when trying to open the Outlook attachment. In this case, the file was called voicemail.mp3 and was caused by the fact that 99 other voicemail.mp3 files had been received as attachments previously. It was as simple as deleting all the attachments in the temporary store and then trying to reopen the attachment.
Of note - an easy way to find the Outlook temp folder is to do a regedit and search for: