Hi

In my case, the solution was changing the Regional Setting of Windows. 

The regional settings that I used to have was Greek. That was creating a TMP file with greek characters in the date, that was part of the name. QuickBooks does not support that, probably because it does not support UNICODE. As a result it is failing reading that file later, in order to complete that backup procedure.

I have changed the Regional Settings of Windows into English and everything works, except that I cannot set the regional settings that I want