Finding what called a subroutine

[Anonymous Monk]

I have an error happening, but I cannot find with any debugging it... whatever is happening is calling a subroutine, so how can I print out the line and file that *called* the subroutine that is executed?

The subroutine is in a file that is in one of the many files, so I don't know which file is generating the error, so I need to track the subroutine and what called it. I have the debugging reporting to me, before it exits out, but I don't know how to check what called it and what file it was in, if possible.

is it even possible?

Thanks,
Richard