We recently had this issue, we had to completely clear all cache files including cookies and passwords. Open the browser, make sure DFM is not the homepage, clear all the cache - files, cookies, and passwords, close the browser, log back in clear everything again, log out, logged back in and it worked. We believe it is the automated proxy script used here, but are not sure. This has cleared up more than 5 separate people having the issue.
Not sure why, but clearing the cookies/passwords for just OCUM/DFM site did not work, might help, might not.