Vault Issues with 15GB SanDisk Flash Drive. Please Help!

I’ve just tried to access my vault on my 15GB flash drive, but rather than just prompting me for my password as it has every other time, I got the pop-up asking me to create a new vault. I entered the same details as I had previously; password etc, as I though it could just be a case of a software update. Now however, the new vault is completely empty. There is no sign at all of my old vault. However, when I look in the \FILES\ 00000000 sub-folder, I do see what appears to be all of my files which are in an encrypted format that can’t be opened.  Please help!