I am having the same issue here. Rooted my Eris last night without any real issues (KaosLegendary ROM). I started messing with the SetCPU setting and things were fine (got it quite zippy, actually). Then I got a phone call and Sense crashed. I cannot do anything, since it crashes and I force close, and then it crashes again repeatedly until I just turn off the phone... The phone is worthless right now as far as I know.
I should say this is my first post and am definitely a noob (though I have had success tracking and troubleshooting on my own in the past)
SetCPU settings were:
Main: 768/480
Screen off: 480/245
Failsafe: Temp 44.3 C / 480/122
Also, had installed a number of apps (Pandora, Dictionary.com, Epicurious, USA Today... and had some widgets running (weather, clock, news, pandora)
Any ideas would be great!
Crooze,
Sounds like your phone may not be stable at 768MHZ.
We also probably need a little more info from you re. what exactly is going on:
1. Did you take a Nandroid backup? (can you restore to a previous, safe state?)
2. Did you enable "set-on-boot" in setCPU? (un-enable it if you can)
3. Does you phone still boot-up? (can you change clock settings in setCPU?)
4. Have you tried flashing a different ROM? (problem with KaosLegendary?)
5. Have you tried posting a question over on XDA in the dev's thread? (you'll have to register there in order to post: [ROM]KaosLegendary V.17 [05/19] [OC] [A2SD] - xda-developers; they are very helpful, but it pays to be polite and patient with the devs
)

.
(i.e., I don't want to suggest anything unfruitful for you to do or do any harm).