Hello from 2019;
The root issue was reported here on github in 2015, doesnt look like emasher is developing anymore.
I just did this on my Tekkit Legends v1.1.1 server. I took the map into a single player world to check and yup; game crashed. A quick MCEdit of the level.dat to remove the Modular Socket and loaded it back up into the single player world; issue resolved.
However when I put this new level.dat into the server world save folder I keep getting the same crash log. Issue pointing back to the modular socket. Has anyone else had this issue for multiplayer?