My only guess is that you just don't have enough VRAM for the actions that cause the error.
Well... if it worked for three months and now it doesn't I'd have to ask... what has changed? Have you tried cleaning your Adobe Cache?
Also, why are you editing in HD in an NTSC sequence? It's really hard work on the machine. A better workflow is to edit at the native resolution, make a native res master and then transcode to whatever else you need. I'm not saying this is the cause of your problem but you are taxing the system and creating a lot more render files than necessary
I think that's good advice. I admit I wasn't aware of the Adobe Cache and went to clean that. I'll see if that helps resolve the issue. I appreciate the suggestion for editing natively, as well. when i got the system i did what i could to get up and running and producing output the way we air it, so that's why i was trying to edit that way. now that i've had some time on the system and understand it's workflow better, i believe your suggestion may work better for me now.
thank you for the advice. i'll post back later as to whether or not the issue i'm having was resolved by cleaning the cache.
Since you say you are new (3 months) Here is a list of Tutorials
A "crash course" http://forums.adobe.com/thread/761834
A Video Primer for Premiere http://forums.adobe.com/thread/498251
Premiere Tutorial http://forums.adobe.com/thread/424009
Premiere Pro Wiki http://premierepro.wikia.com/wiki/Main_Page
Tutorial HD to SD w/CS4 http://bellunevideo.com/tutorials/CS4_HD2SD/CS4_HD2SD.html
Color correction http://forums.adobe.com/thread/892861
After Effects Tutorials http://www.videocopilot.net/
Surround Sound http://forums.adobe.com/thread/517372
Photo Scaling for Video http://forums.adobe.com/thread/450798
-Too Large May = Crash http://forums.adobe.com/thread/879967
-And another crash report http://forums.adobe.com/thread/973935
Encore Tutorial http://www.precomposed.com/blog/2009/05/encore-tutorial/
And more Encore http://library.creativecow.net/articles/devis_andrew/
Regions and NTSC vs PAL http://forums.adobe.com/thread/951042
-and Regions http://forums.adobe.com/thread/895223
And a place to be able to save the PDF user guides to your hard drive
Are you using MPE Hardware and howmuch Ram does the Quadro have?
Your post said that you were moving stills. If the still are way bigger than HD proportions, it can zap your video memory pretty quick. If you don't want to photoshop them to a more managable size, just switch to MPE software mode while you are working with the stills.