gdm error messgae

[Melinda Taylor <melinda phys unsw edu au>]

I have recently enabled XDMCP on my new linux server so that users in my
local network can connect to the server using their xterms.

However I keep seeing the following message in /var/log/messages:

gdm[1241]: gdm_xdmcp_decode_packet: Unknown opcode from host XXX.XX.XXX.XX

All the IP's are valid IP's for xterms in the dept. but I am not sure
exactly what the error message is telling me? ANyone have any ideas?

Many Thanks,

Melinda