I would have never guessed it but developer left out basic form tag.
Since I have been using this plugin for ages with no issues, as is usually the case with Conor's code...this line finally got me annoyed enough to look in the plugin code for tpl_product_info_display.php.
I find these snippets which build the form:
PHP Code:
$form_start_tag = zen_draw_form('back_in_stock_notification', zen_href_link(FILENAME_BACK_IN_STOCK_NOTIFICATION_SUBSCRIBE, zen_get_all_get_params(), $request_type), 'POST'); $back_in_stock_notification_form->setVariable('back_in_stock_notification_form_start_tag', $form_start_tag);
followed by
PHP Code:
print $back_in_stock_notification_form->getXHTMLSource();
So if you are having to manually add in the form code/reinvent this particular wheel, that means the plugin code is not being output as per design, so you need to investigate the conditions:
PHP Code:
if (isset($back_in_stock_notification_build_form) && $back_in_stock_notification_build_form) {
and find out why.