this might be worth trying
When 'Add/Remove Programs' fails, do this to remove Yahoo Messenger from your pc:
CLOSE the Yahoo! Messenger application if you currently have it running. Make sure all instances of Internet Explorer are CLOSED.
Go to your desktop and double-click "My Computer."
Click the "C:" drive.
Go to C:\Program Files\Yahoo!
Highlight the Yahoo! Messenger folder and press the 'Delete' key on your keyboard.
DEFRAG your computer files to remove those empty spaces resulting from the deletion.