add to cart error message

Dear Woo be woo,
I struggle with a problem on my store.
I can’t add to cart more than 1 product (with attribute) from the same vendor.
Example:
If I try to add more than one product with attribute to the cart I have this message:
“Well, you already have some item in your cart. First checkout with those and then purchase other items!”
The problem is that: The products are from the same vendor.
And the message appears just on the tables I created with woo be woo
If I go on the product page, I don’t have this problem.
Thank you. I hope you will be able to help me.

The page I need help with: [log in to see the link]