Exception in world tick

Using the DNS Techpack for all my Mods.

Never had this problem before, seems to randomly crash with these errors.

I have noticed two things;

firstly everyone who crashes on the server crashes at the same time with this error

secondly the people who are crashing seem to be PC users; 4 people on the server, 3 of them are PC users and one of them uses a MAC. The three PC user crash with this error and the mac user has yet to crash.