mod_headers warning

Hello,

I have the plugin activated but “It seems your server setup does not support headers in .htaccess. You should either fix this (install mod_headers) or deactivate the “Enable direct redirection to existing converted images?” option. Otherwise the Vary:Accept header will not be added and this can result in problems for users behind proxy servers (ie used in larger companies)” error.

I contacted the server company and it was stated that mod_headers is active on the server. Although mod_headers is active, I still get this warning and I can’t use the plugin unfortunately 🙁