@
vinieux -
for the detailed explanation, much clearer now.
Everything you did should have worked. In the attached screen shots you'll see calibre 64 bit accessing a library within a Calibre Portable library folder - exactly as you tried to do. And the same library being accessed via the calibre_portable.exe.
I suspect Geek Uninstaller hasn't caught up with MS's latest registry entries regarding Default programs and Open With etc. This issue has been recently discussed in this thread
Install/Uninstall Windows 10 calibre. In particular I draw your attention to posts #2 and #9 from Kovid.
Hopefully they will assist you in getting your Calibre Portable install working again, and in the case of the environment variable prevent the 'unholy mess'/ 'calamities on toast' being created in the first instance.
Two other things to remove before you reinstall 64 bit are the
...\AppData\Roaming\calibre and
...\Documents\Calibre Library (the default library) folders That will ensure you get a virgin install. When you start calibre it will open the default library - there should be one book in the library a Calibre Introduction by John Schembler.
If you take a system restore point immediately before you install the 64 bit version, and things don't work again you could do a system restore back to that state. The 3rd screen shot shows an example, if I did the restore selected, it would put me back to the state before I did the registry edits - including backing out the calibre 2.55 update and reinstating the out of cycle Flash Patch.
BR
Capabilities and Toasts are two of the registry subkey names that contribute to what Kovid refers to as an 'unholy mess' - hence my 'calamities on toast'
