w3 validator

Hi,
the w3 validator give me an error on: http://validator.w3.org/check?uri=http%3A%2F%2Fwww.xhost.co.il
site: http://www.xhost.co.il
Error: Line 872, Column 193: document type does not allow element “link” here
…imonials-widget/testimonials-widget.css?ver=3.4′ type=’text/css’ media=’all’ />

last versions (plugin and wp)

please advice.

http://ww.wp.xz.cn/extend/plugins/testimonials-widget/