Sales quote to Order Assembly order - NAV 2016

Hi Folks -

One of our customers user is trying to use the Make order function from a Sales quote. When they click on Make order, they get a standard message 'Do  you want to convert a quote to order?' and when they say Yes they get the below message. On the Item F220006036 on the Sales quote line they have Qty. to Assemble to Order = 1.  Does anyone know what would be causing this message.  

Any help is truly appreciated.