This looks similar to panics others have posted about... I did
"disklabel sd1" while in single user mode:

panic: pool_get: ffsinopl: page empty
:
_Debugger(...) + 6
_panic(...) + 52
_pool_get(...) + 114
_ffs_vget(...) + 90
_ufs_lookup(...) + a32
_lookup(...) + 21c
_namei(...) + 2e2
_vn_open(...) + 168
_sys_open(...) + 7e
_syscall(...) + 11c
_trap0() + e

-- 
Name: Dave Huang     |   Mammal, mammal / their names are called /
INet: khym@bga.com   |   they raise a paw / the bat, the cat /
FurryMUCK: Dahan     |   dolphin and dog / koala bear and hog -- TMBG
Dahan: Hani G Y+C 23 Y++ L+++ W- C++ T++ A+ E+ S++ V++ F- Q+++ P+ B+ PA+ PL++