I was using MSN then I was disconnected from the net. Then when I signed back in, I got the screenshot.

MSN signed in fine, but msgplus didn't load. However it didn't display the recovery window because it show the floating contacts??

Anyway, I dont why this happens but has happened a few times before and no sure way to reproduce it.

Perhaps it is the floating contacts??

I doubt it. Plus is obviously loaded in some way, it just hasn't hooked the window. Maybe closing and opening it would get the menu back?

If you want plus back on straight away go to My Computer>The main drive(normally C)>Program files>MSG Plus(whatever no.)>and open the MSG.exe. Sorry I don't know how to fix the bug though.

When you open msn messenger, plus! has to load, to fix this go to Plus! > Preferences > General Options > Miscellaneous, and click 'Force Messenger Plus! to Load on Startup', you should no longer get this problem again as plus! will load whenever your pc is started and run constantly.

If that doesn't work then:

This can also be caused by Windows Messenger starting up in the background. Go to your processes (CTRL-ALT-DEL) and check if the process msmsgs.exe is there. If so, then have a look here on how to prevent it from starting up:
CookieRevised's reply to I am about to rip my hair out over MS Messanger