When I run my program (admittedly, it was built in debug mode), I get an error \"External exception 80000003\".
According to Win32 Exception/Access Violation Errors
A breakpoint is essentially a machine level instruction (opcode?) that causes the CPU processing to pause and an exception type signal raised. This is usually picked up by the OS and then onto some user process like a debugger or simillar.
When I've had this it's nearly always been when my code as jumped into some data space. I say nearly always as I've hardcoded breakpoints into code accidently when debugging some nightmares occasionally too (!).
Edit: As @Ken White says int 3 (the breakpoint interrupt) is the one I used to hard code :-)
First thing I would do is get a stack trace and work backwords.