Roaming Profiles Broken

Hi folks. We are having some trouble with roaming profiles. 90% of our users seem to be fine. But I have a handful of people on a handful of machines that are having trouble. When they log on, it will give an error (security error) and it will fail to load their profile, and it will create a temporary one. It doesn't do this every time however. If they continue to try, eventually it will let them on usually. Since it has been some what inconsistent, I am having a hard time narrowing it down to a computer, network, or user problem. Everything was working fine last spring, but when the staff got back this fall the problem appeared. I am wondering if one of the recent updates perhaps broke roaming profiles? Has anyone else run into this yet? Nothing else has changed on our network and it only seems to effect certain machines and certain users.

If I rebuild the users profiles it seems to help, although it hasn't fixed the problem... I am busy putting out lots of other fires, so I haven't had a lot of time to devote to this yet, so I wanted to see if anyone else was experiencing this problem?

Thanks.