added some vars in category.php but doesnt work on server

I added some variables like $data['subcategory_products'][] into controller\product\category.php, it works on local test XAMPP server but those variables cannot be invoked on production server. VQMOD installed on both local and production server.

here is the error msg:

<b>Notice</b>: Undefined variable: subcategory_products in <b>/home/xxx/public_html/catalog/view/theme/xxx/template/product/category.tpl</b> on line <b>51</b><b>Warning</b>: Invalid argument supplied for foreach() in <b>/home/xxx/public_html/catalog/view/theme/xxx/template/product/category.tpl</b> on line <b>51</b>

Why? How to fix it? Thanks!