Just thought I would add some things I found out.... When I downloaded the new Yahoo Messenger I got the same error that many were getting, "Uncaught exception java.lang.error," but I also ran into the problem that the Yahoo Messenger Icon disappeared all together. I read in one of the forums that if you go into Options> Applications and delete Yahoo and then re-install it would fix it. Not so, after trying over and over, resetting my whole phone, it still didn't work. Here is the trick. While in applications, press menu, select Modules. If the net_rim_yahoo module is still there you have to delete it. Once the Application and the module is deleted, then re-install Yahoo Messenger. Once that is done, follow the instructions in the first post of this thread and you should be good to go. As always, this worked for me, but I am not responsible if it messes up anyone elses phone. Good Luck!

Instructions for AT&T Pearl and Yahoo Messenger 2.***
1. Back up your Service Books using Desktop Manager
2. Delete the Yahoo Messenger Application:
Select Options > Advanced Options > Applications
(Dependig on the Theme you are using this may be different)
Scroll to Yahoo Messenger (Could be listed as net_rim_yahoo)
Press the Menu Button and select Delete
3. Verify that the net_rim_yahoo module is deleted
In the applications menu, select Menu > Modules
Scroll down to net_rim_yahoo, if it is there, select Menu > Delete
4. Let the phone restart
5. Re-install Yahoo Messenger
6. Follow the steps in the first post of this thread to load the correct Service Books

Hope this helps.