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) identifies a URL resource whose actual media type 1) does not agree with the media type specified on the request or 2) is incompatible with the current data for the resource or 3) is incompatible with the HTTP method specified on the request.
Detecting exactly what is causing this problem can be difficult, because there a number of possible reasons. Often the request involves transfer of data from the client to the Web server (e.g. a file upload via the PUT method), in which case you need to confirm with your ISP which media types are acceptable for upload.
This error seldom occurs in most Web traffic, particularly when the client system is a Web browser.
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 media type specified by the client system.
Our service monitors your site for HTTP errors like 415. 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. The content of the HTTP data stream we send is plain text, and the HTTP data stream we expect back is a simple byte stream. Both data streams make no reference to any specific medium.
Please contact us (email preferred) whenever you encounter 415 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 '415'.