A friend of mine is also having this problem.. He tried a couple of times but still can't register as if his email address/IP was blocked; I was able to register perfectly though.
If it can be of help, I can post his IP/email address (maybe via PM to the staff)
Anyways, I hope the problem will be fixed soon, too.. not only for him, but I wish you can figure out what it is and sleep with more ease after all the debugging! ^^