If I remember, I had the same trouble when I tried to register. It turned out that the register page uses a higher encryption level than most of these services on the Internet.
You have already sent a money order but for those that have the same problem, check your security encryption level. For MS Internet Explorer users, click “tools” in the menu bar, AOL open “Settings/Internet Options” and find the link “use your Internet Explorer settings…”
In the IE options window click on the “Advanced” tab all the way to the right and scroll down to “Security”. You will find two check boxes for “SSL 2” and “SSL 3”. By default only SSL 2 is checked. The Brainbombers register page uses SSL 3 and will reject your submission if you aren’t using it.