Indeed it was a key mismatch, I reset my RSA key, moved the pub over to the server, and everything is working now. Thanks much!
Ok, now that I have the right port defined for the firewall (22), I've gotten further along. Now the client immediately gives the following...
I found the tutorial on setting up x2go on Ubuntu to be very detailed and well-laid out, with substantive screenshots and a thorough process....
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