When I'm trying to select Payments extension I receive an error:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<p>You don't have permission to access /admin/index.php
on this server.<br />
<p>Additionally, a 404 Not Found
error was encountered while trying to use an ErrorDocument to handle the request.</p>
All other extensions work smoothly. What is wrong?