The Web server (running the Web site) thinks that the HTTP data stream sent by the client (e.g. your Web browser or our CheckUpDown robot) contains a 'Range' request which specifies a range of bytes which can not be satisfied - because the resource being accessed does not cover this byte range. For example if the resource - an image file for example - has 1000 bytes and the Range requested is 500-1500, then it can not be satisfied.
This error seldom occurs in most Web traffic, particularly when the client system is a Web browser. The URLs in this case are typically standard hyperlinks found on Web pages, which very seldom use the 'Range' specification.
If your client system is not a Web browser, the problem can only be resolved by examining what the client is trying to do then discussing with your ISP why the Web server rejects the 'Range' specification sent by the client system. Most often this is due to a badly written client system which uses the 'Range' specification but disregards the total size of the resource being requested.
Our service monitors your site for HTTP errors like 416. This error should simply never occur on your CheckUpDown account. If it does, it typically indicates defective programming of our systems or of the Web server which manages the site. We do not use the Range request at all, because we always want the entire content of the URL you ask us to monitor.
Please contact us (email preferred) whenever you encounter 416 errors - there is nothing you can do to sort them out. We then have to liaise with your ISP and the vendor of the Web server software to agree the exact reason for the error.
Any client (e.g. your Web browser or our CheckUpDown robot) goes through the following cycle when it communicates with the Web server:
This error occurs in the final step above when the client receives an HTTP status code that it recognises as '416'.