Hi all,
In case it helps anyone else who is totally frustrated... Seen other posts on this too, but one more doesnt hurt.
For me the solution quite clearly was the
RequestedNumThreads
setting in the UserSettings.txt file that did it.
Default seems to be "-1". Start trying with "0" and increase until you get trouble.
In my case I have a AMD "Bulldozer" type cpu, and I suspect that ESO thinks it has more "physical" cores than it actually has, and creates enough threads to get into trouble. Also I still run Vista which might also contribute.
For me the magic number seems to be "3", and my cpu has 4 "real" cores.
Good luck!