I'm having the same issue and even had a few messages lock up during scrolling, I tried a battery pull and cleared the event log, went back to the same message and it still locked up.
Posted from my CrackBerry at wapforums.crackberry.com
same thing happening here too. Hoping to hear from a "wise one" to show us the way. I had the issue where it locks up and won't allow me to scroll up with only one of my contacts but I closed out of the convo, and started a new one with him and it continued to do it. No idea why. Help us!