On DM go to Backup and Restore, select Advanced. Scroll down to 'Browser Cache' - highlight it, and click the button to move it to the left (File Side - button looks like << ). If you encounter an error with that, then select OK, highlight the Browser Cache database on the right side, and Clear it.
Your device should now backup properly, unless there are more (or other) errors in other databases.
You can sorta guess which DB is having problems by how far along the normal backup process it gets before it errors out, then you have an idea where to look in the list of databases. I copied several from right to left before I found the Browser Cache was the culprit, which I had thought could be true based on the multiple threads I found on it using the search feature.
I tried that and had problems with other DBs. I eventually weeded out the bad ones, but will I never be able to do a full backup without picking and choosing?
Once you clear the offending DB's, you can either start from scratch, or use one of your older backups and hope that something between the last backup and when you started having the errors was the problem.
After I cleared the browser cache DB it worked fine on a normal backup.