What JVM are you using? Sun or MS? If SUN, check to see if you have the following dlls in your system32 folder:
stas651.dll
stsm651.dll
stfm651.dll
http://www-1.ibm.com/support/docview.wss?rs=899&uid=swg21202719
If this is an invited meetings issue, take a look at:
http://www-1.ibm.com/support/docview.wss?rs=899&uid=swg21163315
Hope those help.