 <p>Thank you again for your quick reply Amitesh.</p> <p>I checked the file "modules/Accounts/metadata/subpaneldefs.php", and I find that there is no array('widget_class' => 'SubPanelTopSelectButton', 'mode' => 'MultiSelect') in the declaration of $layout_defs['Accounts']['subpanel_setup']['opportunities'] array, so I add it manually and it works now.</p> <p>There is also another alternative, this one consists of deleting the subpanel and creating a new one.</p>