A patch is something that changes Messenger, like adds things or take things away, like buttons, text, etc. So if you don't know what one is, I doubt you've used one.
Errrm.. try
Microsoft Update, make sure everything is up-to-date.
Also, any idea what you may have changed 2 months ago that could have caused this? You could use System Restore, or even just look on it and you could see what changes you made 2 months ago (If it's enabled, you should be able to). You can do this by going to Start > Help and Support Center > Undo changes to your computer with
System Restore.
You can then see what changes you made on a certain date: