subporduct is not adding into cart in woocommrece product bundle

I am using woocommerce Product Bundles extension and I have a parent (bundle) product with two sub-products.

1 of them is simple product but other is variable product having 2 attributes and 12 variations

I am having difficulties in adding parent product into cart due to this variable product.

I get this error "PARENT_PRODUCT" cannot be added to the cart. Please choose "SUB_PRODUCT" options…

that is weired because for this sub product I have set variations defaults. and if I add this sub product individually it adds to cart successfully.

anyone know what I am doing wrong?

via Chebli Mohamed