Both of you share this theory, so I suppose it isn't groundless, but it is inconsistent with the nature of the error message itself. The message "Text file busy" is a system error message given exceedingly rarely and under very specific circumstances.

He was running Linux, you're running FreeBSD, so it's unlikely an OS thing or a filesystem thing. "Perl 5" doesn't help nail down a common version there (5.00503? 5.004? 5.6.0?).

Try doing what he did when you get this error message. Try just copying the file to a new name and copying it back (using a simple 'cp'). If the problem goes away, it's very unlikely that it has anything to do with the content. If it doesn't fix it, then it could possibly be content-related.

So if we eliminate the OS, eliminate the filesystem (by eliminating the OS), and eliminate the content, the only thing left is the "way" that the file was saved or a bug with Perl. We'd need to do more investigating.

If you have 'strace' or 'truss' on your system, I would be very interested to see precisely what syscall is involved in that error message. If it's acting on a file descriptor, back-track until you can find the open statement involved.