Index: wp-admin/includes/image.php
===================================================================
--- wp-admin/includes/image.php	(revision 6287)
+++ wp-admin/includes/image.php	(working copy)
@@ -39,6 +39,8 @@
 			elseif ( $type[2] == 3 ) {
 				$image = imagecreatefrompng( $file );
 			}
+			if( ! $image )
+				return;
 
 			if ( function_exists( 'imageantialias' ))
 				imageantialias( $image, TRUE );