A customer has been using my app for a few months and today my app
starts freezing on them. I have madExcept embedded into the program
and it generates error reports like this:

exception message : The application seems to be frozen.

main thread ($304):

ntdll.dll NtWaitForSingleObject
ws2_32.dll select
fbclient.dll gds__alloc
fbclient.dll _isc_event_block
nCall.exe IB_Events 782 +18 TIB_Events.API_Register
fbclient.dll isc_que_events
nCall.exe IB_Events 803 +8 TIB_Events.API_QueueEvents
nCall.exe IB_Events 576 +15 TIB_Events.RegisterEvents

This is happening on all their PCs (8 of them). All report a similar
error to the above. This has worked fine for the past few months and
nothing of note has changed.

Any pointers about where to begin tracking this down?

I'm running BCBv5, IBOv4.3Aa, FBv1.52

Thanks

David