Product Options / Variants

Hi, I need to have product options/variants but cannot get it work with Group Deal or Open Deal. I had posted this issue at OpenDeal project page but no answer.

To add product options I use the plain commerce way, so admin has to create couple of related products (product type) then create a product display ('Deal' content type) to show them. But everytime I change the Number of Values (product field at 'Deal' content type) to Unlimited (or any value above '1') the page is shows error:
Fatal error: Call to a member function value() on a non-object in /public_html/mysite.com/profiles/groupdeals/modules/custom/groupdeals_module/groupdeals_module.module on line 166

Example for product options/variants:
Theatre X voucher has options:
• VIP Seat $500
• Front Row $200
• Mid Row $120

Beauty Salon voucher has options:
• Cut Only $100
• Cut + Blow $200
• Spa $120
• Cut + Spa $160

Selling T-Shirt (Physical product) has options of:
• Size S $15
• Size M $20
• Size X $25
• Size XL $30

How do I apply product options/variants ? I would appreciate any suggestion and help. Thank you.