I tried to install chap-secure-login.1.4 plugin, by going to Plugins > Add New > Browse and adding the zip file, like it asks for.
Then it says it has successfully installed. But it is not showing in my list of Installed plugins. It also does not show in my Plugins folder in Filezilla FTP. But if I try to repeat what I did, it says folder already exists!
I have done it this way for other plugins and it worked fine. The other way of manually uploading unzipped folders has never worked successfully for me either.