406 Not Acceptable
When a browser makes a request for data from a server, the server returns an “Accept header” to the browser that made the request. The browser will respond to the request, stating the formats in which it is able to accept data.
If a server is unable to send data in the format in which it received the request, the server will return a “406 Not Acceptable” error.
This error code is only seldom displayed to the general user, as the error message will very rarely be understandable by general users. Instead, most servers will ignore the relevant header and will instead send the user an actual page.
A 406 error can be caused by mod_security
A 406 error can, however, also be activated if Mod_Security has been activated on an Apache web server. The program runs on the server and scans for non-compliance with the configured rules. If an action occurs that is not permitted on the basis of the configured rules, the server will return a 406 error.
The problem with 406 error pages
When a page returns a 406 error to a user, it leads to a very negative user experience. A standard Internet user is unable to do anything constructive with the error message, which will normally lead to the same experience as a user who has encountered any other type of error page.
Poor user experiences can damage your websites reputation and can discourage potential regular users away from the site.
An excessive error page frequency, including 406 error pages, can lead to serious visibility problems for your website. Search engines (including Google) detect and interpret the various error pages and if their frequency is excessive, this will affect the overall qualitative assessment of the website as a whole.
Google has various different penalties for low quality, including “Panda”, “Phantom” and “Fred”.
The value of external links value will be lost
If external links on the Internet direct to 406 error pages on a website, the link value which would normally be transferred to the site to which they link will be lost.
How should you deal with 406 error pages?
As with other error pages, 406 error pages need first of all to be identified and action must then be taken on the pages which report 406 errors.
Normally, the best solution in relation to error pages is to redirect them. However, you should be aware of the fact that a 406 error may well be browser-based, i.e. directed at a specific browser. You should only redirect pages if they report an error that affects multiple browsers.
301 redirects are the recommended solution for redirecting pages, because a 302 redirection does not instruct search engine crawlers towards permanent relocations, only temporary ones.
301 redirects allow link value from external links to the 406 page to be redirected over to the new destination URL.