I was just placing down a bunch of Adv solars when this happened. Its not the first time it happened, and the utter lack of information in the stack trace is leaving me befuddled on where to report this.

And it seems to happen randomly.

http://paste.ee/p/2d9Tm

Yeah- it doesn't actually link to Mekanism anywhere. It may just be one of those corner-case Minecraft issues. If you somehow trace it directly to me I'll definitely take a closer look.