dashboard and site warning after upgrading to 2.9

Have you tried:

– deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the default theme to rule out any theme-related problems?

switching to default or any other theme gives the same problems, with classic and default even an extra error:
Warning: Cannot modify header information – headers already sent by (output started at /home/creatief/domains/domainname.nl/public_html/wp-includes/rewrite.php:790) in /home/creatief/domains/domainname.nl/public_html/wp-includes/pluggable.php on line 868

i’ll now try the plugins and upgrading on another site.

got it. the plugin job manager makes trouble. After deactivating it, no more errors/warnings.

wp-includes/rewrite.php line 788:
$posts = get_page_hierarchy($wpdb->get_results(“SELECT ID, post_name, post_parent FROM $wpdb->posts WHERE post_type = ‘page'”));

either “get_page_hierarchy” or “$wpdb->get_results” can be null or empty if the blog have no page at all.
so, i think its wise if we check $posts before feed it to array_reverse.

line 795:
if ( !$posts )
return array( array(), array() );

for short solution, i think we can move line 95-96 in the ealier lines before array_reverse.

I implemented this solution and it was successful.