3 things you could quickly check:
1) are these TCP ports reachable from client to the server:
TCP 42342
TCP 43242
>> you can easily test it with e.g. telnet 42342
if they are unreachable, check for any firewall on the client and server the could block the communication (e.g windows firewall, virus scanner with embedded firewall, etc.) or check Access-Lists on the gateway, etc..
2) is the hostname of your LMS server resolvable from the client
>> just ping the servers' hostname
if not, check your DNS or add the name to the clients hosts file
3) if the above is ok, check for the correct Java version and just use the one provided with LMS
>> it is available on the LMS server in NMSROOT\htdocs\plugin
