When you go into Audit Trail Viewer, if you are not registered then you will see a label telling as much. You need to click on the link to send through your details to us and we will set you up with a licence.
Normally after this point you can also go to the Raiser's Edge Tools menu, Run DLL Macro and then select the "Show Audit Trail Version" macro to run. This ought to tell you that you are registered.
What happens if it does not but Audit Trail Viewer does not show the "not registered" label? i.e. they are giving you conflicting messages.
One cause of this is because the Server Configuration Module has been set up but points to an incorrect database. It may point to a non-production database for example whereas you are working on the production.
Trying running the server configuration again, login to the production database and ensure that the server configuration points to that same database.