Now I see .....  I was looking for the lack of a definition for "BusinessClassController" not a blank field.

So now that I have none that meet your definition. Where do you suggest I look next. I am deleting modules one at a time on a /localhost copy of the production system, clearing the log, wait a few hours and checking for exceptions. Looping thru this will take a while but it should isolate it to a module, IF it is a module.

/DaveS

All of those -1 entries for User, Portal, etc. indicate that it is the Scheduler producing the errors.

Search Indexing in the scheduler is usually what causes this.  Try turning off scheduled items one at a time to see when it stops. I would start with the Search Indexer.