It's been a long time since I installed WHS 2011 on an EX485 but I think I remember the 31 exit is that it can't find the system disk even though it found it once and did a format. I think I fixed it by going in and disabiling the SMI boot process under HP in the bios. The only thing that uses it is Whs v1 recovery, so it's no problem for you. The EX485 has some problems with the boot priority and I think the smi is the culprit.
HP EX470, 4 GIG, 4200+ EE SFF, WHS V1, Production
HP EX485, 4 GIG, E5800, WHS 2011, Stablebit Drive Pool, Transfer Server, Backup Server
HP EX490, 4 GIG, Q9400S, WHS 2011, Stablebit Drive Pool, Mediaserver
HP EX485, 4 GIG, Q8200S, WHS 2011, ITUNES Server