Admin CP error message ‘Couldn’t open plugins directory’

Earlier, I activated the ‘One Click Plugin Updater’ plugin. It gave me the option to upgrade all my plugins at once. I selected it and now the plugins control panel gives me this error “Couldn’t open plugins directory or there are no plugins available.’

I deleted all my plugins and then downloaded wordpress 2.5.1 again and uploaded its plugins folder. I got the same error, so I re-uploaded the plugins.php file in wp-admin and the js file in wp-includes.

There are plugins in the wp-plugins file, but the plugin management panel is still not recognizing them.

Any ideas how to fix this?

Thanks.