The cause of reg hive becoming to large

I’ve read Microsoft’s articles re: recovery system.ced and what others have reported on TechRepublic, but do we know why this happens or what causes it. I support a trading floor and the image we use on our trading machines Win2k Pro is standard throughout. One user, however about every week or so, his system crashes and he gets this system.ced error so we swap out the machine using the same standard trading machine image — it’s faster than using recovery. We are driving ourselves crazy trying to determine the cause and why only one user gets this registry hive too large error. We’ve increased the Reg to max 128.