VAST error 201, aka Video player expected different linearity, is an error that can be caused when the linearity in the buyer’s response does not match the video player’s request. For example, if a non-linear ad was sent in a response when a linear ad was specified in the request. To fix the error, the publisher should ensure that the correct linearity is specified in the ad request and the buyer should ensure that the response only includes linearity specified in the request.