I have been racking my brains trying to figure out why my CA2A  would not register.  I tried reinstalling, clearing registry entries and various other ill fated attempts to resolve the issue.  The guy who helped me  could not figure it out instantly either, but he was patient and gave me confidence it would get resolved despite being a total mystery. 
 
My problem?  Turns out that I still had the PC2A installed. So if any of you somehow have PC2A on your system and purchase CA2A, remember to uninstall it first.