Just out of interest - has this problem been solved for you yet? - I had the same issue finding AD2 in Sonar platinum, eventually found the .dll file under:-
 
C:\Program Files (x86)\Steinberg\VstPlugins
&
C:\Program Files\Steinberg\VstPlugins
 
I mapped the VST scan paths to search both these locations & now AD2 shows up in Sonar as expected - but a lot of the replies above helped me sort out the problem (it's been a long time since I set up new software)

Did you completely uninstall the previous version of Sonar when you reinstalled? As in, not just CONTRON PANEL - UNINSTALL SONAR, but deleting ALL traces in the registry?