4.00.235 is the newest version:
* The previous versions required Windows XP SP1 minimum to run, this version can run on an unpatched Windows XP machine.
* Fixed another problem that caused Messenger Plus! Live to fail to load on some computers for no apparent reason (bypassed an internal requirement that is not valid anymore with Windows Live Messenger Final).
Please update and see if the problem continue:
http://www.msgpluslive.net/download/