The error message is from the base ESO files (not files from a specific addon) so it's pretty much impossible to track down with just that.
- What addons do you have?
- When does the error message show?
- Can you try disabling addons to isolate which addon is causing the problem?
(NOTE: don't disable 1-by-1, but disable half at a time and it'll be much quicker. Ie, if you have 20 addons and disable 10 but the problem's still there, you know it isn't from the 10 you disabled. So now you just need to look at the 10 remaining.)