Ah!

My eye's are starting to blur at this point, I confess.

I would suggest simplifying things and then building back up to your timers.

ISEXCLUSIVE is a red herring. Sorry, I thought you meant that you had a table open that you thought you had used exclusively.

Anyway, yes, if you USE sometable EXCLUSIVE your ON ERROR routine will fire if it's in use elsewhere. You'll have to keep trying to USE the table exclusively until you get a lock.

Wouldn't FLOCK() be more straighforward? Maybe that's my bias, though.