Have you tried uninstalling and then reinstalling? Sometimes a firewall or other security software can interfere with your online registration. Be sure to disable your security software prior to reinstalling. I cannot speak for the developer's absence in replying to you; I can only offer advice to help get you up and running.
(Did you use 'Support' from inside AllMyBooks to contact the developers?)
Please let the forum know whether or not this advice helps in your situation. If not, we'll try something else.