Unable to backup phone - fails every time!

[Landsharkk]

I have a Lumia 920 on whatever the latest OS version is from AT&T.

Occasionally my phone pops up a notification, "Haven't backed up in a while, backup now?"

And every time I attempt to backup the phone it fails. No error details, just a 'failed to backup'.

I've tried doing after rebooting. I've tried with no apps running, etc. I've tried when connected to WiFi and when only on LTE.

Anyone had this issue or have any suggestions?

I'm hoping to get a backup done before upgrading to the 950 or 950 XL.

Thanks!