zfs code - Mar 2008 - assertion failed: dn->dn_nlevels > level (0x0 > 0x0)

Occasionally when importing a pool with encrypted datasets it in we see 
this failure.

Interestingly though we can''t reproduce this on demand.

Any ideas on what it is I''ve likely done that causes dn_nlevels to be 
wrong ?

panic[cpu1]/thread=ffffff04e01c7180: assertion failed: dn->dn_nlevels > 
level (0x0 > 0x0), file: ../../common/fs/zfs/dbuf.c, line: 1567

ffffff001ee15660 genunix:assfail3+b9 ()
ffffff001ee15700 zfs:dbuf_hold_impl+33a ()
ffffff001ee15740 zfs:dbuf_hold+2b ()
ffffff001ee157d0 zfs:dnode_hold_impl+bd ()
ffffff001ee15800 zfs:dnode_hold+2b ()
ffffff001ee15880 zfs:dmu_buf_hold+45 ()
ffffff001ee15950 zfs:zap_lockdir+60 ()
ffffff001ee159f0 zfs:zap_lookup_norm+56 ()
ffffff001ee15a50 zfs:zap_lookup+2d ()
ffffff001ee15ac0 zfs:dsl_pool_open+94 ()
ffffff001ee15b80 zfs:spa_load+574 ()
ffffff001ee15be0 zfs:spa_tryimport+99 ()
ffffff001ee15c30 zfs:zfs_ioc_pool_tryimport+3c ()
ffffff001ee15cb0 zfs:zfsdev_ioctl+162 ()
ffffff001ee15cf0 genunix:cdev_ioctl+48 ()
ffffff001ee15d30 specfs:spec_ioctl+86 ()
ffffff001ee15db0 genunix:fop_ioctl+7b ()
ffffff001ee15ec0 genunix:ioctl+174 ()
ffffff001ee15f10 unix:brand_sys_syscall32+197 ()


-- 
Darren J Moffat