I managed to figure out why i was getting two separate errors on two different websites while the plugin was working ok on others.
In the wp-config.php where you get the code
define( 'WPCACHEHOME', '/PATH/wp-content/plugins/wp-super-cache/' ); //Added by WP-Cache Manager
The actual line of code the plugin writes on installation is:
define( 'WPCACHEHOME', ' /PATH/wp-content/plugins/wp-super-cache/' ); //Added by WP-Cache Manager
If you look closely at the two lines you'll see a small detail that seems to break the path to wp-super-cache, it's an empty space in this place: ' /PATH
That's why some people had success activating the plugin after reinstallation, because sometimes it skips the empty space and writes: '/PATH
How come no one figured this out till now!?
After figuring out the problem on my first website, which was getting around 5 erorrs, i went to my second one which was getting some exec() error, closed the gap and the error was gone.
Right now, i believe close to every path error people have comes from that gap in the code.
Maybe you shold write this in the FAQ if you can't fix it.