I keep seeing this crash every so often, no custom Buildings just stock stuff running in lightweight/minimal mode.

RecurrentComplex-1.3.1.1
http://vpaste.net/MyfBL

Same. Besides that, the console keeps spamming this: Skipping BlockEntity with id minecraft:rcspawnscript

Didn't test it but this should fix your problem. Let me know if it's not fixed (in 1.3.1.2).