Could you give some more details on what's going on? I just tried setting a background image and it came back up just fine. Are you using background images? Also what format are they? What version of NetSight are you running?
Hmm.. I just tried this with a jpeg image on 188.8.131.52. I'm not seeing any problems after saving it and reopening it. I would suggest opening a case with GTAC to see if they can help troubleshoot your problem.