HTML Guide for chrome=1

A “meta” element with an “http-equiv” attribute whose value is “X-UA-Compatible” must have a “content” attribute with the value “IE=edge”.

The only value admitted for the attribute content in a <meta http-equiv="X-UA-Compatible"> is currently IE=edge. You’re probably seeing this issue because the page being validated includes the following meta tag:

<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />

As the Google Chrome Frame plugin was discontinued on February 25, 2014, this is longer supported so you should change that meta tag to:

<meta http-equiv="X-UA-Compatible" content="IE=edge" />

According to this article in Wikipedia:

Google Chrome Frame was a plug-in designed for Internet Explorer based on the open-source Chromium project, first announced on September 22, 2009. It went stable in September 2010, on the first birthday of the project. It was discontinued on February 25, 2014 and is no longer supported.

The plug-in worked with Internet Explorer 6, 7, 8 and 9. It allowed suitably coded web pages to be displayed in Internet Explorer by Google Chrome’s versions of the WebKit layout engine and V8 JavaScript engine.