Azure Backup failing with 0x07EF8

So I set up azure backup on the 4th, it backed up successfully once and has failed every time since.

It's bombing with a generic message unable to find changes in a file, code 0x07ef8

I've found a few threads with the CBEngine, CBUI and CBCmdlet logfile location, I can't find any filenames that it can't access in those, antivirus is stopped and it's still failing with the same error code.

Where else can I look to find out what's blocking this?

Thanks!