Ye olde permissions error

Getting the “Warning! Could not update /path-to-wordpress/wordpress/wp-config.php! WPCACHEHOME must be set in config file.” & “Warning! /path-to-wordpress/wordpress/wp-content/advanced-cache.php does not exist or cannot be updated.” errors. “wp-content/advanced-cache.php” does not exist, so changing permissions should have fixed this. It didn’t. Also changed permissions on wp-config.php and temporarily moved it in its default location; still no joy. Tried to follow the instructions re: editing /plugins/wp-super-cache/advanced-cache.php, but they aren’t very clear, or the code has changed since they were written.

“Change the text CACHEHOME to /path-to-wordpress/wordpress/wp-content/plugins/wp-super-cache/” OK, but the file has 4 instances of WPCACHEHOME, not CACHEHOME. Am I supposed to replace all of them (except the commented one) with e.g., WP/path-to-wordpress/wordpress/wp-content/plugins/wp-super-cache/? Because that is literally what the instruction say to do.