We have recently upgraded our WAN links to 1Gb, so I would like to start consolidating servers at our central office. I am trying to configure the network to allow PXE across the WAN for ZENworks imaging but I am getting an error that Google hasn't been able to help me with ;-)

Currently the remote router is configured with two ip-helper statements, one to the central DHCP server and one to the PXE/Imaging server (they are separate servers). When I PXE boot a workstation here's what I see:
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CLIENT IP: 10.2.10.71 MASK: 255.255.0.0
DHCP IP: 10.0.2.5 PROXY IP: 10.0.5.75
GATEWAY IP: 10.2.1.20 10.2.1.1


Auto-Select:
ZENworks Boot
PXE-E78: Could not locate boot server
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Do I need to set any extra DHCP options for PXE to function? The only other person I found with this problem fixed it by enabling spanning tree portfast on their switch, but we aren't using spanning tree so I don't think that will work for me.