Sorry to hear that you're having problems with UltraReverb in Ableton.
-Are you using the AU or VST version of UltraReverb?
-What directory is the plug-in located in?
-Can you send us/post here the crash report so we can see what is happening?
We can get you an older version of UltraReverb in the meantime. Send an email to firstname.lastname@example.org mentioning your issue and my name, and I can send you an older version.