Something I wrote a trouble report about:
Up until a very recent Sonar version, I had only 32-bit Sonar installed. After I installed 64-bit Sonar for the first time I got many scanning errors and plugin-not-found errors when I ran earlier projects in 64-bit Sonar. It was caused by an error in the registry: The value for "VSTScanPath" in "HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR\Cakewalk VST X64" pointed to the 32-bit version of VstScan.exe in Program Files (86).
That might be something to check ...