I had this problem after deactivating wp-super-cache. You need to delete the files from htaccess that were written by wp-super-cache. They may still be there and causing the issue.
You can use the file manager in cpanel of your hosting to do this. There will be something that says begin wp-super-cache and something that says end wp-super-cache. Delete starting from wp-super-cache and ending with end wp-super-cache.