Win8.1 and admin account for registration

I believe that you need to launch Sonar as administrator by
-right click the Sonar icon
-choose run as administrator
 
Then you will be able to enter the codes. Normally Sonar can be run without Admin privileges, but for registration, Sonar needs read/write access to the registry. Once it is properly installed, you should not need to run it as Admin as a general rule. There are some Soft-Synths like Pentagon that require you to run as Admin however.