--- class/piCal.php
+++ class/piCal.php
@@ -2257,7 +2257,7 @@

        // カテゴリーの処理
        $_POST[ 'categories' ] = '' ;
-       $cids = is_object( @$_POST['cids'] ) ? $_POST['cids'] : array() ;
+       $cids = is_array( @$_POST['cids'] ) ? $_POST['cids'] : array() ;
        foreach( $cids as $cid ) {
                $cid = intval( $cid ) ;
                while( isset( $this->categories[ $cid ] ) ) {