@limelect I appreciate your suggestion and understand where you're coming from.
I don't think it's necessary to take those steps because the application is currently running on thousands of machines without a problem.
So far it is only two machines and as of this morning having tried the most recent machine I cannot get a repro again.
The affected window has not been edited in four years so there haven't been any controls added or moved etc.
I'll keep hunting,
Cheers, Aidan.