Backup error 103

SOLVED

Good morning

We have an issue where we are unable to backup the company due to a file that I'm guessing has corrupted? I've attached a screenshot

This particular invoice was created about 11 days ago and our accountants tell me in order to delete it, they'd have to re-do the last 2 weeks work manually.

Is there any alternative solution to this?

This same error popped up when emailing the relevant document to the client at the time of creation.

Regards

Michael