I tried logging into MSN Messenger a couple of days ago and got an error saying that I had to download the latest "Windows Live" version. My current version is 7.5 and I don't want to download the latest because I hate it as it is a memory hog.
After searching a few forums online, I found the following workaround to get MSN Messenger 7.5 logging me in again:
Right click the MSN Messenger icon and select Properties
On the Compatibility tab choose to Run this program in compatibility mode for: Windows 2000
Click OK
Now, when you start MSN Messenger, it reinstalls/repairs it and then allows you to log in again! Only thing is, you end up with a funny icon in your System Tray.