Ping to and from

I can ping from a workstation with NT4 to a Citrix-Winframe-server in the same local network. But I can’t ping the other way around. The subnet is equal. The only difference I can see is that the Citrix has a default gateway (the router). Citrix canping to this router (the ws can do this too) and it can ping another NT-server that is in this local network (as can the ws as well).
Anybody any suggestions.
Thanx
George