A few things that might be the cause...
- Are you using Messenger 2011 in compatibility mode?
- Are you using any other Messenger add-ons or patches like: A-Patch, MessePatch, SweetIM, Smiley Central, Kiwee, Messenger discovery, MSN Shell?
- Any other apps which are known to cause problems like: GDI++, ThreatFire, PC Tools Spyware Doctor, Bandoo, HiYo, Kingsoft, Internet Security, AirFoil, MapleStory (MMORPG), BabylonIM?
- Have you tried uninstalling Messenger Plus! -> Uninstalling Windows Live Messenger -> Re-install Live Messenger -> Re-install Messenger Plus!?
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