Adding a post results in 403 Forbidden

After uploading a WordPress website to Etisalat server, I’m getting the following error when adding a new page or eidting an existing page:

403 Forbidden

You don't have permission to access /website/wp-admin/post.php on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I tried adding SecFilterInheritance Off to my .htaccess file but it results in a 500 Internal Error.

I looked at other posts in this forum, and found some people saying that adding a PHP.ini file fixed their problem. But they never say what should be in it.