site error

Hello, I tried your plugin but have not used it lately and would like to disable or remove it until I need it again. However, when I disable it I get this error on every page of my site. If I go a step further and delete it I still get the same error. Once I go get the plugin again and activate it the error goes away. I’ve done this multiple times with the same result each time. Can you help me fix this, please?

Error: Warning: Invalid argument supplied for foreach() in /xxx/xxx/xxx/xxx/wp-includes/class-wp-list-util.php on line 151

Line 151 and a few more”
foreach ( $this->output as $key => $value ) {
if ( is_object( $value ) ) {
$newlist[ $key ] = $value->$field;
} else {
$newlist[ $key ] = $value[ $field ];
}
}

The page I need help with: [log in to see the link]