Gateway test is good for verifying network connectivity, but if both devices are on the same subnet and regularly pass traffic to each other, they should exist in each other's ARP tables. "arptabShow" is the 3300 shell command, I don't remember what it is in MSL but it should be something similar. If one is missing from the other, maybe get Wireshark running on the subnet and verify you see ARP requests going between the 2 when you attempt to connect? Sounds like one of the devices is sending its traffic somewhere it shouldn't, and it's most likely a simple IP networking config problem, like a bad gateway address or subnet mask.