"FORGE ID MISMATCH. HOW DO YOU FIX IT?"

I recently started a server for the FTBLite 2 pack. Runs fine for me but my friend can"t get on. I scoured google looking for an answer and came up with deleting the config folder to regenerate it or manually sync it. I tryed deleting the config folder. No dice. Then I tryed to manually sync it. No dice. The only other way I know of off hand is to copy the server config into the clientside folder....BUT you can't directly edit the server files here......, SOOO my question is what do I do now, HOW DO I FIX IT ?

Yes, we're playing on FTB Lite 2

Alright I gave up and installed Tech World 2. Now the server is frozen. All it says is "Starting". It doesn't start up and then periodically it says its Offline

This afternoon I tried to install another mudpack and got the same thing. The readout in the console just freezes up and the server is stuck at "starting". I can't shut it down. I tried to reinstall it, nothing. I tried to install Vanilla 1.8.9, nothing. Idk what to do next

OK thank you. I appreciate the help