Per JHop:
Since it's happened again in a totally different
workbook, and since that kind of fix is very tedious and not necessarily
guaranteed to work, I'm wondering what could be happening and how best to fix
it now and prevent it in the future. I'd appreciate any help.

FWIW, I've seen similar situations in my own MS Access VBA. Not
resulting in a loop.... but definitely branching to someplace not
specified in the code.... maybe 2-3 occurrences... and they've
all been at the Exit point.
--
PeteCresswell