After installing Windows Vista Service Pack 2 (SP2) Windows Live Messenger 14.0 may no longer start.
If Windows Live Messenger 14.0 was running when you installed Vista SP2 it may run until you exit the program. Once you exit Windows Live Messenger you will not be able to start the program again. If Windows Live Messenger is installed when you installed Vista SP2, Live Messenger will not start.
This issue can occur after Windows Live Messenger detects that an operating system upgrade has been installed and then attempts to perform a repair of Live Messenger. When this occurs Windows Live Messenger tries to use an incorrect Microsoft Installer package.
Please follow these steps below :
To resolve this issue download and re-install Windows Live Messenger:
1. Visit http://download.live.com
2. Click on the Download button
3. When the file download dialog pops up, click on Run to launch the installation wizard
4. On the "Choose the programs you want to install" window you will see Messenger under "This program will be updated"
5. Click on Install and complete the installation
6. Launch messenger and this time it should run fine
Important: Do not attempt to uninstall Windows Live Messenger before you re-install.