SEF URLS

[immune]

After installing sef i get this error . i have read alot of topics before posting , no .ht exists , but i still get that error , what do i do wrong ?

Forbidden
You don't have permission to access /thumbnails.php on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

[Joachim Müller]

Disable the SEF_URL and get rid of the .htaccess file that the plugin created within your coppermine root folder.