Can't see a JetDirect 170x

[dmg2206]

I'm trying to set up a new computer to use an HP printer (LaserJet 4250) we've got networked via a JetDirect 170x external. The problem is that for whatever reason, this particular computer cannot see the JetDirect. It can't find it on Network Neighborhood, and can't ping the IP address. It can connect to every other computer on the network, and every other computer on the network can ping the JetDirect server and use the printer. I'm at a loss as to what is going on. Any ideas?

 

[hpwizzard]

On the external JetDirect there should be a small test button.
Press and hold it for a couple of seconds while connected to the printer and a testpage containing the IP of the box should get printed on the LJ 4250.