I don't think this has anything to do with ASC and Arturia products. With the availble informations it does'nt look like it has.
Message:
D:\VST64 Plugins\Piano V2\unins000.exe
The specified path does not exist
The uninstaller is installed where the standalone application is installed. That's not the same as the VST. So it look like you also have changed the install path for the standalone application, and installed that in a folder you have named. Or how else do you get this path? Why have you done that? And have you set the same path for VST2 plugins?
Use separate paths.
Are you sure the external drive have failed - like in is broken, and that it's not just because the drive letter has changed? I suggest you check that.
If you can't access the external drive in any way, then perhaps you can try to download and install the software again. But this time install everything on the C drive. Then perhaps you can try to uninstall, and that might remove the old installs too from the registry, so it's a s clean as possible. And then install the software yet again on the C drive.
I would try this myself, but i can't tell, if it will work. If not, then you need PC support.
You can download the installers from Arturias website, if you don't have them allready:
https://www.arturia.com/support/updates&manualsI see no reason to install any of the instruments on other drives than the C drive. I suggest you use that. You don't save much disk space using an external drive. It's not huge sample libraries you install. And lot's of stuff including VST3s and presets and more will be installed on the C drive anyway. You just make things more complicated installing the programs on other drives than the C drive. Only do so, if you know excactly how to handle that.
In ASC, when you click an instrument on the home page, then the instrument page open, and in there you can find a green uninstall button down the page to the right. But again, as you have path issues, then it can't find the uninstaller.
Are you new in working with music applications? Do you have and use other music software? If so - is that software installed on a external drive?
BTW: There should be no need to use CCleaner. Unless you know excactly what it remove, then i suggest you don't use it.
One should be careful, when messing with the registry.
Using windows own tools to maintain the system should normally be enough.
CCleaner can't remove software it can't find either. And if you only have used it to clear registry files, then it should'nt do that for installed programs unless you tell it to do so. It would remove the registries then, but not all other files.