I work in IT at a community college and I now have a second user that has had the same issue. When they are trying to attach a file to an email in Outlook 2013 with their Exchange email account, it appears to attach normally. When you go to send the email, however, they receive an error stating that the "file location cannot be found". At least some of the files are located locally on the machine, and the users both are set as admin on their respective machines.
I have tried Outlook safe mode, disabling Outlook extensions/plug-ins, creating a new profile in Outlook, repairing Office 2013 install, even re-installing Office 2013. The only thing that seemed to make a difference was re-imaging the computer, which leads me to believe it's something with how Windows 7's Windows Explorer (specifically file paths) and Outlook 2013 interact.
I actually, initially had a small success by changing the way I navigate to the file. At first, I was navigating to the file using the "Favorites" links in the "Insert File" window. I changed to navigating to the file manually through "Computer" then "C:" etc., in the "Insert File" window. It seemed this had something to do with the answer since I was able to send a few files that way, but even that started giving me the same error, or at least would not reliably work.
Does this sound familiar to anyone, and if so, any guidance as to the cause and solution to this issue? I would like to avoid re-imaging the computer if possible.