Do you have error when you trying to enable WP-Super Cache like this:

Warning! Could not update /home/xxx/! WPCACHEHOME must be set in config file.

Warning! /home/xxx/ does not exist or cannot be updated.

1. If it already exists please delete the file first.
2. Make /home/xxx/ writable using the chmod command through your ftp or server software. (chmod 777 /home/xxx/ and refresh this page. This is only a temporary measure and you’ll have to make it read only afterwards again. (Change 777 to 755 in the previous command)
3. Refresh this page to update /home/xxx/
If that doesn’t work, make sure the file /home/xxx/ doesn’t exist:1.1. Open /home/xxx/$wp_cache_file in a text editor.
2.2. Change the text CACHEHOME to /home/xxx/
3.3. Save the file and copy it to /home/xxx/ and refresh this page.

Trying those steps but still got the problem? The solution is simple, just change file permission to 777 for wp-config.php, refresh the page and change back file permission to 644