During my setup of KCauldron (yes I know it's deprecated), I encountered a rather odd bug. I tried passing extra java arguments to enable a garbage collector with specific settings, and the console gave a jar argument help screen, I checked the process list, and saw it was using a command line switch to pass arguments AFTER the -jar switch. I tried running that command directly, and got the same error. The problem resolved itself after I changed the server settings to Forge, as it used the standard java startup. I'm not sure if KCauldron natively has a command line switch for passing arguments after the jar is specified, and if it does, that means the one I used is an unofficial continuation. If needed, I will try to track down the specific version, I THINK I have the downloaded zip file still, so I can provide it if needed.

There is one more thing I should mention, I'm using the McMyAdmin 3 module for this. I have an amp license as well, but I need to save it's uses.