Does any body know what this means, or how to fix.

Absolute telnet is Version 6.28
Running on Windows Server 2012

This is an indication that the server and client cannot agree on a suitable algorithm to use when doing KEX (Key Exchange). At the beginning of the connection, client and server exchange lists of supported algorithms and one is chosen from the list. If server and client have nothing in common, the connection cannot proceed and this is the error that you get. If this is something you got suddenly on a server where you never had a problem, then something in the server configuration changed. System administrators may have recently removed algorithms perceived as being weak, therefore causing this error in clients that have no remaining algorithms in common. I've been working on some improvements to Absolute to help combat this issue, adding new key exchange and message authentication algorithms as specified in RFC4419 and RFC6668. If you'd like to take it for a spin, grab the latest release candidate here:

http://www.celestialsoftware.net/beta-testing

Brian