P.A.C-4.1.2 - Incredibly Paranoid (PACMAN) ROM - System UI has stopped working (fix!)
I installed this awesome app, and was enthusiastically tweaking it with UI adjustments when I was suddenly hit by "Unfortunately, System UI has stopped working." This flew me into a panic. This popup message looped constantly no matter how many times I pressed OK, and made my phone unusable.
Long story short, I found a solution. Others had had this problem, and posted it on a different android forum. What causes this bug is turning off Quick Settings in the Notification area. Turning it back on again in Settings > System solves the problem.
I was very reluctant to go back to gingerbread after finally finding a good, fast jellybean rom for my Incredible 2. I have reported it, and I do hope it is fixed soon.
I hope this helps!