Running an ASA5505, tried 7.2.4(30) and (33), set up a dhcp relay server, as of this morning clients couldn't obtain new dhcp leases. Did a "debug dhcprelay event 255" at the console, saw this message which doesn't seem to be documented anywhere:
dhcpd_rcv_callback received udp error 2
Did a packet trace on the outside interface of the ASA, saw DHCP discover/offer packets being sent forwarded from the ASA and then received back from the DHCP server as expected. Changed to a different DHCP server and the error went away, clients were able to obtain leases.
The problem appears to be with the DHCP server itself, but the server admin can't find anything wrong with it. Wondering if anyone can clarify what the above error message means so it might help us find the problem on the server.