Index: wp-admin/includes/file.php
===================================================================
--- wp-admin/includes/file.php	(revision 41035)
+++ wp-admin/includes/file.php	(working copy)
@@ -132,6 +132,9 @@
 	if ( ! $levels )
 		return false;
 
+	// Remove the trailing slash
+    $folder = untrailingslashit( $folder );
+
 	$files = array();
 	if ( $dir = @opendir( $folder ) ) {
 		while (($file = readdir( $dir ) ) !== false ) {