I have recently had some DHCP issues at two sites that are bizarre. Whe upgraded the network and introduced Vlan's. Their old dhcp scope was disabled/deleted and a new scope was introduced for the user Vlan. I added a IP helper address in the Vlan and at first the DHCP works fine, but a couple of minutes later it stop's dishing out addresses and only when you reboot your PC it gets an address again. I have done wireshark traces and can clearly see all the broadcasts for DHCP request but you never get the address. Only when disabling that dhcp server and moving it to a server that is not a domain controller it works fine.
I'm no domain controller expert but surely that sounds like some policy or security not allowing the new subnet or something. Even a stupid little wirles AP's dhcp server works fine but not the old domain controllers. Any Idea what to check on the domain controller?