Hi merleneh,
Thank you for your response, and my apologies for the late response.
So that we can investigate this further with you, could you confirm the exact error you are getting? Also, could you please provide a screenshot of that error when it occurs? Is the file you are trying to back up stored locally on that computer, or is it being accessed across a network?
In some cases, we have seen files opened across a network experience issues similar to what you encounter when trying to back up a file that has been opened across a network. To resolve this, you would either need to access the file and back it up on the server or copy the file onto that computer and open it from there to back it up.
Please let me know if you need further help.
Cheers,
Princess