Default Safestrap backups not working

Im using ss 3.72. My phone version is NB1. And I always use the stock slot.

Anytime I make a backup of a custom rom and try to restore back to it at a later time...IT always fails when it gets to the part where it says "restoring system".

This wasnt always the case in the past. Why is this happening now?

Any help is appreciated, thanks in advance