When I failed mine in December 2008 NCEES gave us an extension in January (by two weeks) provided you mailed them a copy of your fail letter with the app verifying why you are applying past the deadline, someone asked this before and I told them my experience and another user got really rude...
Well I failed the April exam (took it in Alabama) and I HAD to send acopy of my fail letter to apply for the October exam because our results came back AFTER the deadline, it was the only way we could get an extension on the application.
They give those who fail extra time to apply for the next test, you have to send in a copy of your fail letter and you can register during the late period they provide!!!! But good luck :) maybe you wont have to worry about all that!!!!