Mine also locked up after installing over the top. I uninstalled and reinstalled the new rc2 and everything is working fine now. WinXP PRO Dell GX110
Here are some stats that I found interesting. With RC1 the first time I ran it (aggressive mode) it cleaned 3118 keys, and a day later an additional 470.
I ran RC2 in aggressive mode and it found 297, it corrected 9 and removed 135. Thats 144 out of 297. So I ran it again and it found 26 keys and the fix removed 26 keys. On the third run it found 4 keys but they were all the mru so no problem. Still don't know what happened to the other 127 keys.
So far, including the previous cleanings under RC1, I have had no problems. This is my primary system at work, so it gets a lot of use.