Find out what is causing 406 Not Acceptable error in WooCommerce

I have a website running WooCommerce and a plugin called Fancy Product Designer.

When I installed on a working website I got a 406 Not Acceptable error once the design had been completed and I click Add to Basket.

I make the design, select the variable product and then click add to cart. http://prntscr.com/lw8tv7 then get this http://prntscr.com/lw8tjb

I have created a brand new install of Wordpress and tested but I get the same error.

I need someone to take a look and tell me what the problem is.

Thanks