get message "400 Bad Request" after opening "Tool Station" on the internet. I use this site on a regular basis and this is thefirst time his problem has occured

I have been on to "Tool Station.com" to order products on line which I have been doing for many years. Today half way through from trolley to check out, the following message has come up. "400 Bad Request. Browser sent request that this server could not understand. Size of request header field exceeds server limit". Unfortunately this is "double dutch" to me. Please help.