The update to 2.4.2 introduced a problem with Thaumic Energistics - Applied Energestics 2, which caused certain ME systems to crash the server when their owner logged in/loaded it. We know this was a major inconvenience, and we apologize, though it was through no fault of our own.
The good news is, the problem has been addressed, and the exceptions are being caught before they can cause a crash now. All who were previously banned are now free to log back in with no changes to your setups or bases.
We can't wait to see you in game :).