I suspect that on your Linux client machine you are using a configuration file (nxplayer.cfg) created on Windows. Could that be possible? If this is the case, the nxplayer.cfg file on your Linux host will have the SSH Client key set to nxssh.exe:
You can check whether this is the case by:
$ cat nxplayer.cfg | grep nxssh
If you get:
<option key=”SSH Client” value=”nxssh.exe” />
change it to:
<option key=”SSH Client” value=”nxssh” />