File in use error

Hi,

I'm using Dell DataSafe Online (1.1.0023) on Vista64. It's been working ok for a while, but this week-end, when trying to do a back-up, I kept getting an error: "The process cannot access the file because it is being used by another process". Of course, it doesn't say which file (or which process) -- not very helpful. I've tried rebooting, having all other programs shut down, and then starting the back-up, but the error still happens. 

Thanks

Jimmy