Please make sure that you have entered your VAT no. in the correct format. Every VAT no. must begin with the code of the country concerned and followed by a block of digits or characters. The amount of digits can vary, depending on the country.
Please find more information here.
Does it still not work? There might be a temporary problem with the EU VAT validation service (VIES) that causes a problem. Please wait and try to complete your order later, or contact the NCS Colour customer service.