I have never actually seen a 406 error before. But a quick google pointed me to:
A client (e.g. your Web browser or our CheckUpDown robot) can
indicate to the Web server (running the Web site) the characteristics of
the data it will accept back from the Web server. This is done using
'accept headers' of the following types:
Accept: The MIME types accepted by the client. For
example, a browser may only accept back types of data (HTML files, GIF
files etc.) it knows how to process. Accept-Charset: The character sets accepted by the client. Accept-Encoding: The data encoding accepted by the client e.g. the file formats it understands. Accept-Language: The natural languages (English, German etc.) accepted by the client. Accept-Ranges: Whether the client accepts ranges of bytes from the resource i.e. a portion of the resource.
Fixing 406 errors - general
This error occurs very infrequently in Web browsers, because most browsers will accept data returned from the Web server.
If the client is not a Web browser, then anyone can only
investigate the problem by looking at the Accept headers generated by
the client system and the data stream returned by the Web server. If you
do not have access to the source code for these systems, the only thing
you can do is refer the problem to technical support people at the
companies that developed the systems.
quote source: http://www.checkupdown.com/status/E406.htmlI would check the mime types that you have on your server first.