Cannot negotiate KEX with 3rd party - "No appropriate prime between 1024 and 1024"

[dverbern]

Hello,

Using VShell 4.4.3 (x64 build 1966), a 3rd party is failing to connect to VShell - seems to be failing during KEX whereby "diffie-hellman-group-exchange-sha256" is selected, but then logs show error:

"The transport was aborted with a disconnect packet: No appropriate prime between 1024 and 1024 is available."

This issue appears to have been occurring for some time, and may date to when I had upgraded our VShell version - but this is the first I'm hearing of this issue from this particular 3rd party.

VShell currently has the following Key Exchange Algorithms checked:

diffie-hellman-group-14
diffie-hellman
diffie-hellman-group
diffie-hellman-group-exchange-sha256

I can indeed see a 'primes.txt' file within the VShell directory on our server, but not sure what to make of its contents.

Can someone please assist me in overcoming this issue?