I have some fresh installs today but it is gave me an issue:
The server was not able to find the document (./cgi/addon_softaculous.php) you requested.
Please check the url and try again.
I guess what should happen is that the install happens and redirects you to addon_softaculous.cgi but this fails.
If you reload the main plugin page it then links to the .cgi
And seems to work ok afterwards