Shoutbox

Windowsblinds is basically a program which lets you change the theme and style of your computer. It's been known to have some clashes with Messenger Plus! in the past. Your lack of knowledge about it leads me to the conclusion that it's not that causing the problem though because it's simply not on your computer (I must be a genius)

Anyways, from that image the circled area isn't the only problem - the tabs at the top are spaced but too large a margin. I'm guessing there's something wrong with the xml settings in Plus! (which basically sorts out the layout).

Have you tried reinstalling Plus! to see if this will install correctly? If that fails, you may want to try clearing your internet cache and re-downloading Messenger Plus! Live and try again.