Do you have a web part on every page  that may be having a problem? Are any of the web parts on the page which show up in error on the web part page?

Does the problem stick around after the server  is rebooted?

Is this one of your production WFE servers?

Yes, production. All front ends eventually get the same error, usually after approx 250,000 sessions. No answers yet, IISReset will fix temporarily. My dev, test and non-LB portals are are fine.

One interesting note, I suspect it is WSS related because 50% of SPS works.

This might deserve a call  to PSS just to see if they have seen something in the performance of WSS that causes this. Otherwise, I don’t have an immediate answer for you.

We had some strnge issues when moving from test environment to production environment.

Test Environment had 2003 Sp1 and production didnt have! Discovered it later, since test environment was setup and 'handed over' for a project with some serious deadlines! So in production environment, I applied Wss SP2 and it resolved the issue on hand. However after few days, we had some other strange issues. PSS advised SPS SP2 as step one. That resolved our issues and we haven't looked back...

Test, Dev and production are 3 existing, seperate environments. Sites are built and then moved via stsadm. It seems to happen directly after being crawled by the index server, go figure.

We don't have an answer from Microsoft yet, but if/when we do, I will make sure and let everyone know.

We are running  Win2ks, SPS-SP2, WSS-SP2. Enabling NetIQ Security Manager exacerbates the issue, so there ya go.