g_ufs_done() WHAT does it mean?

[Bob Falanga]

I have installed freeBSD on a SATA 320 gig hard drive. After running for a
few minutes I get several of the following error messages:
g_ufs_done():ad4s1d[WRITE(offset=385482752, length=16384)]error=6.
After two pages like that the computer stops and requires a hard boot to
restart.

I assume that the messages concern the hard drive, but what are they telling
me?

Help, and thanks,
Bob Falanga