Index: wp-admin/upload.php
===================================================================
--- wp-admin/upload.php	(revision 11613)
+++ wp-admin/upload.php	(working copy)
@@ -267,7 +267,7 @@
 		continue;
 	$arc_row->mmonth = zeroise( $arc_row->mmonth, 2 );
 
-	if ( $arc_row->yyear . $arc_row->mmonth == $_GET['m'] )
+	if ( isset($_GET['m']) && ( $arc_row->yyear . $arc_row->mmonth == $_GET['m'] ))
 		$default = ' selected="selected"';
 	else
 		$default = '';