Hopefully someone here can help me as I've nearly gone crazy trying to fix this. I was building in a Feed The Beast Ultimate server I run and accidentally middle mouse clicked on a RedPower Wireless Transmitter, my game instantly crashed. Apparently this is a fairly common problem, but my searching hasn't turned up any working solutions. I've tried editing my player.dat file with NBT edit to remove the offending item, when that didn't work I deleted my .dat file to see if that would refresh my character on that server which didn't work either. I've tried re-installing my client and each time I see a flash of the inventory I had pre-crash.
You have three options here, Feed The Beast is a very buggy game, so you probably had a crash due to ram, try applying more ram to the application, re-download the application or try to find the redstone problem in-game, up to you dude, good luck.