Pasha Siraja

So I am running a teeny tiny Tekkit Lite server and have 4 of us players on it. I have always, since the beginning of my Tekkit life, have been able to run up to 4 to 6 instances of tekkit modpacks, same ones and different ones at the same time on my machine with the same and different legitimate minecraft accounts all the time. Now, I try to run a SECOND account while playing tekkit lite for chunk loading/checking remote things in-game, and the game wouldn't launch while one instance is running ? Why ? :'( If there is a work around to this, please tell me. Yes I HAVE Googled it and couldn't find a working solution to it. Please help me get multiple instances of Tekkit Lite/Other modpacks working with different minecraft accounts at the same time ! Thanks !!!