The following three workarounds are suggested.
1) When you have the installer of the same version, open a command prompt and type the following command:-> setup.exe /uninstall
This should uninstall the client completely.
2) To turn UAC off, follow the steps below.
a) Click on the Start button >> Control Panel >> Search box(right side top)>>Type "UAC".
b) Click on Change User Account Control settings.To turn off UAC, move the slider to 'Never notify' position and then click OK.
c) Administrator permission is required to make this change, so if you're prompted for an administrator password or confirmation, type the password or provide confirmation.d) You will need to restart your computer for UAC to be turned off.
3). You can download and run the Microsoft utility Microsoft Fix-it to fix the problems that block you from uninstalling a program.This utility will also help you to fix corrupted registry keys. You can download this utility from the link-
http://support.microsoft.com/mats/program_install_and_uninstal