At this point, since NullPointerExceptions are hard to nail down (at least for me, who doesn't know Java), I'd recommend a Tekkit reinstall. Save your waypoints (rei_minimap folder), and just delete your entire Tekkit folder. If that still doesn't work, and this is your server, go delete your player.dat file from the server files. You'll lose your inventory and XP, but you'll be able to play, most likely. If it isn't your server, you'll have to work something out with a server admin to do that. I don't know what other advice to give.