Encountered Improper Argument Error

Hi,
 
I'm semi new to  Sonar and totally dig it.  I've been running mega sessions (live rehearsals - 12-15 tracks) for several takes - no problemo.  Playback CPU usage tops at 3-5% if I have the vintage channel on the master bus or a couple of plug-ins running.  Smooth as silk for 6 months!
 
Last night when playing back a new session (8 audio drum tracks) I encounterred a dialog box "ENCOUNTERED IMPROPER ARGUMENT". When you click the okay button, nothing happens, the playback continues and the only way to stop it was to turn off the PC! The only effect  running was the vintage channel in the mix bus.
 
I deleted the session in my folder and started a new session, and I am a-okay now.  Does anyone know the cause of this error message.  I wouldn't want this to happen if someone is paying me!!
 
I am running a new sweetwater creation station with windows XP @ 32 bit @ 44.1 16bit -Quad Core-3.65 Gig Ram - RME Multi-face 2 - Frontier Tango 24-metalfalke bongos and red vines. 
 
Thanks for any help!
 
Chuck
Drool Brothers 

I think its some windows generic error message. If it doesnt happen again, then it could be a flook or flouk or flouk or floock.
Are you running XP SP3. Try updating to it