I play D2 on PC (Steam). Ever since the Into the Light update, I've lost count of how many times I've received an error code and was either a) kicked to the D2 login screen, or b) kicked back to desktop because of game crash.
Most of the time, I don't get any warning about "Contacting servers...", I just instantly get kicked out of an activity into a black screen with the error code at the bottom (mostly its Anteater, sometimes its Weasel), then after a few seconds it either goes back to the login screen, or the game crashes/closes with no further info or popup of why the game crashed.
I've power-cycled my modem/router. Nothing has changed with any settings on those devices, or my PC. My NAT Type in game is always "open" via port-forwarding. I've done the "Verify integrity of game files" in steam, and I've even uninstalled and reinstalled the whole game. After all of this, I still receive error codes after about 5-6 waves in Onslaught. When I load back into the same activity, it happens after about another 5-6 waves.