iMac does not boot

Good evening!

I have a network of 200+ iMacs with 2 GB of RAM, a 2.66GHz Intel Core 2 Duo processor, and OS X Lion (10.7.5). Recently, I've noticed a number of them failed to boot properly. The iMacs pinwheels at the Apple logo screen and never boots to the login screen. This has recently occurred after staff has logged in to their network accounts. Troubleshooting has revealed that one of the frameworks fails to launch, therefore causing the boot strap to crash. Here is a screenshot:

If that framework is missing or corrupt, I wonder if replacing it with a working one would cause the iMac to boot. So far, I've been re-imaging the machines to rectify the issue, but seems to be only a temporary fix. The same issue appears after a day or two. I'm not sure how it's caused. My guess is that when re-imaging these machines, via NetBoot, the partition gets corrupted during the process. Another theory is that there's something in the user's folder that causes this problem. I would like to know what steps I should take next? So far, I've tried repairing the disk and repairing permissions.