While connected to a remote site via IPSec VPN, I was able to login to the web interface without a problem. I clicked the "Launch Java KVM Client" and downloaded the familiar JNLP file "viewer.jnlp(192.168.0.jnlp". Opening the file displays the Java loading screen, and a prompt to tell me it's downloading and starting the application - great. The "Connecting to KVM Server" prompt appears, but immediately after, a "Login failed" dialog box which ended the application.
After doing some Google'ing I saw other people experiencing the same issue but with no solution. I made sure there was no firewall policy blocking the VPN connection from accessing the default Java KVM port of 2068, and that there were enough available sessions (with a max of 4 sessions, 0 were active). I opened my favourite packet analyzer and tried to determine where the connection was failing, and I noticed that my username was being sent as 1234567890 and my password was 0987654321.
Opening the "viewer.jnlp(192.168.0.jnlp" in a text editor showed the offending lines below:
Simply editing the user and passwd values to what I used to login to the ThinkServer Management Module, saving the file and re-running the new, altered "viewer.jnlp(192.168.0.jnlp" file let me connect with no problems.
It seems as though the downloaded JNLP file was just a generic file that was ignoring my session credentials, and I expect it will be fixed in a firmware update, but for now I have my modified file which works as expected.