Ubuntu hangs in NoMachine on Amazon EC2

I am using CAELinux on Amazon EC2 from Windows XP

I can start the instance, connect with putty, log on and change password just fine.

I can then logon with No Machine client and it all comes up and works like a charm.

After about a minute or so the client hangs. Cursor still changes to ubuntu one as I hover over the window but I cannot do anything and sometimes it says (Not Responding) in the title bar.

In windows task manager I can kill the client and then restart and relogon and it brings me to the exact point it hung, but I can do about a couple minutes more work until it hangs again.

There has to be a setting somewhere that I'm missing or not setting or is my connection dropping. I am at a loss here what to try. Any help is greatly appreciated.

Thanks,
Miles