It's a pity that you have to read this page but here we are :/
Take a look into the
log/ directory. MCL and it's monitor both log into their own log files. Most errors will be visible here. You may also take a look into the minecraft server log directory.
Edit your configuration and activate
debug mode at the very bottom. This will output more debug information and also full stacktraces for exceptions to the log files.
Sometimes it is easier to run MCL in the foreground when debugging errors especially if you are restarting MCL a lot. To run MCL directly and not daemonize the process run
This is for advanced users only. Switch to your MCL directory and run MCL with the following command:
You can now issue
!mclshell ingame and use the interactive shell to debug the problem.