I have quite literally just upgraded to Corel Paint Shop Pro Photo X2 and have now noticed that CCleaner reports some (not all) of the file associations used by Paint Shop Pro as unused, despite files of the reported types all working and opening fine on double-click. The output is identical the problem reported here, except of course I'm using CCleaner 2. If I do perform the clean it removes the associations and they must then be re-enabled from within PSP.
Fortunately(?) I know a reasonable amount about the structure of the Windows Registry to work out what seems to be going on.
This new version of PSP is only registering it's file types under HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts and not in the main HKEY_CLASSES_ROOT as previous versions of the program did and indeed how many other programs do. Below each extension under the FileExts key (i.e. HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.jpg) there exists another (new?) key named 'UserChoice' which itself contains a REG_SZ string value named 'ProgID' which holds the name of the key to be found under HKEY_CLASSES_ROOT.
I must say I've not noticed this kind of behaviour in previous versions of Windows, maybe I wasn't looking hard enough, as you'd usually expect the extensions to be registered under HKEY_CLASSES_ROOT, but I've checked, double checked and triple checked and everything works just fine with file extensions registered this way. I can only assume that this is a new perfectly legitimate way to register file extensions in Vista, possibly as a way to play nice with UAC which restricts access to the HKEY_CLASSES_ROOT (TrustedInstaller and Administrator Users only), and CCleaner just needs to be made aware of this new functionality.
I hope I haven't left anything out. If you need any more details or information I'm willing to play Guinea pig and test things out or send you dumps from my registry, etc.
