Simple 3x3x3 Reactor. I went from the top down using a TiC Hammer doing a 3x3 Block aoe break. The server crashed instant with this error:
http://pastebin.com/z9EDMV6N

Sorry I tried repeating without luck again in MCPC/None MCPC Environment without Luck.

Weird. Should be a relatively simple fix for the symptom, but I can't be sure what the cause is.

Thanks for the report.