Googling for
Code:
pftcl: DIOCXCOMMIT: Device busy
returns only one reported problem, the source of which was an incorrectly upgraded system; the kernel and userland were incompatible. So one possible reason for the error is a Frankensystem. You might want to ensure your /sbin/pfctl and your kernel are from the same -release.
If you are certain your software is in sync, the next step would be to grep through the pfctl and PF source code to determine the logic that would produce the message. You will find pfctl(8) source in src/sbin/pfctl, and pf(4) source in src/sys/net.