There are a few possible reasons why your registration won't go through.
Registered email address
SpinPals only allows one single account per player - please make sure you don't already have an account, if you do, you will not be able to create another one.
If you are not sure whether you already had an account, and have forgotten your login details, try to recover your information using the Forgot Password? link on the home page.
Accessing from a restricted territory
One possible reason why you are unable to create an account, is that you are currently in a restricted territory where SpinPals is not accessible.