Hi, I'm having the same issue for days, and after a little bit of reserching, an user of the same pack had the same problem. I proceed to detail it.
First of all you are with some gregtech machines, and you connect a LP mk1 to a fluid solidifier. Then you connect a LP satelite pipe. You install a module upgrade and a fluid crafting upgrade. You give the satelite pipe a name, and use it in the mk1. Destroy it and replace it, but don't give a name. When you try to reopen the mk1, your world may crash.
The first time it happened to me, it says that was an error or LP, then of GTCE and then FastWorkbench.
I also put the link of the user to have a log, and some more information.
FTBTeam/FTB-Interactions#1309
it has also kind of a solution, but is a little bit anoying, you can destroy the satelite pipe with MCEdit, and you can then reopen your world.