I can't connect to GPUMAX, either. It appears that GPUMAX changed my worker's username unannounced, so I've tried to use both the old and new username, with "abc123" as the password, as that's what the dashboard tells me to use. I then created a new worker, and I tried that new username. None of these work.
I've tried to follow this thread closely, and I don't see any explanation beyond the IP range locking. Is this still being worked on? When should I expect to have GPUMAX usable again?
Also I think you're using a blacklist. In this case it is appropriate that the support clarifying the facts.