This type of behavior usually indicates a problem with an incorrect DLL or some other support file. It could also be caused by an improperly configured peripheral that is used by NetMeeting such as a web cam or multimedia board.
Start with going through everything you have installed recently. One of those packages probably stepped on NetMeeting.
Try running sfc/scan to see if the Windows File Protection system identifies any out-of-date NetMeeting files.
Then try de-installing and re-installing NetMeeting. Get the most current version from Microsoft's web site.
This was first published in July 2001