Windows 7 HP.
A few days ago I started having troubles with Windows Live Messenger: it would start fine, but when I signed in, it would sign me out a few seconds later. There are a number of home grown fixes on the internet but none worked for me. Finally I found an official site of solutions which included a list of problem .dll's. I found one of them in an application I recently installed called ShopSafe. Uninstalled that, and voila, WLM works again.