Once you have identified the base problem that is causing the symptoms, try to reproduce it in your test account.
Also, establish a list of probable causes. Once you have a list of all of the probable causes, use your technical knowledge to prioritize that list. Your list should have the probable causes listed from most likely to least likely. Incidentally, be sure to question the obvious. For instance, if the symptom is an error uploading a document, have the user lost the Internet connection? Additionally, if no probable cause can be determined, you will need to escalate the problem to FutureVault support by creating a ticket.