I have this same problem when I enable more than 1 cpu (freenas 8.2 release p1 64 bit, in an ESXi 5 guest)
Everything works very well with only 1 virtual cpu enabled.
supermicro H8SCM-f mainboard
AMD opteron 4170HE
16 GB ram
1 LSI 3081e-r
3 seagate st3200641as sata drives
ESXi 5 host