Add Virtual and Simple Products to cart

Question

I had developed an ecommerce site. I have both simple and virtual products in my site.so when i add simple product to cart and then i add virtual product then i am getting the following error.

Nominal item can be purchased standalone only. To proceed please remove other items from the quote.

I think we cannt add virtual and simple both at a time.

please help me how to add both to cart at a time.