"Sorry, this product is unavailable" error???

Hello, I have a Woo commerce theme and shopping cart and I sell custom t-shirts. On my site I have different drop down tabs that allow the customer to select color, size, style, etc. of the shirt and then when they finish the price should pop up and they should be able to pick quantity and add to the cart. Instead, It says “Sorry, this product is unavailable. Please choose a different combination.” this only happens on the products that have the variations. There is not quantity issue and I’ve checked all the variations and nothing has changed I do not know why all of a sudden it does not work can you please advise?