Error in upgrading MSN MESENGER from 7.0 to 7.5

Hi, i recently upgraded my msn messenger from 7.0 to 7.5. the 7.5 one worked
perfectly. However, the old 7.0 version stays in the system. When i tried to
uninstall it through add/remove program, it wont allow me to uninstall it.
Instead, i get 2 messages. The 1st one says something abt 'error id 1635' and
the 2nd one says somethings about patch error and it asks me to redownload
from the internet. I have tried everything, including google, system restore,
anti virus scan, anti spyware scan, and reinstaling the 7.5 version. Nothing
works. Any help will be appreciated. thx