checklink: Error: 406 not acceptable

I am now getting Error: 406 not acceptable when I try to check my 
links pages. What is the explanation for this?

e.g. http://www.minimarcos.org.uk/links/marcos.html

This used to check OK.

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|_|. _   Richard Porter               http://www.minijem.plus.com/
|\_||_                                mailto:ricp@minijem.plus.com