Broke/breaking - as in using a stop statment at the entry of the event sub routine, like a red code break for debugging.
You are telling us it does something like a breakpoint on entry to the BeforeUpdate event routine entry point.
Assuming you did NOT intentionally put a breakpoint in that context, if a debug window comes up you should be able to use the Locals window to look at the Err object to see Err.Number and Err.Description. Or you could use the Immediate window to use a Debug.Print for Err.Number and Err.Description, and that would probably be very helpful.
VBA doesn't just "stop" - it stops for a reason. Programming is deterministic and highly predictable. So most of the time you just sail through that point and nothing unusual happens. But when it stops at that entry point, my first guess would probably have been a bad parameter and you somehow have turned off warnings so you don't get an error message box to tell you the error. But then, this is an event routine, probably coded by a wizard, so won't contain a linkage error. The only parameter for the BeforeUpdate event is Cancel, which would be hard to mess up unintentionally if the event code was created by the appropriate wizard.
I didn't realize from your original description that you meant that your code breaks as in breakpoint. So many folks tell us their code breaks meaning some other type of error notification or event. Sorry I didn't catch your drift right away. Sometimes I'm denser than other times.
