Tidy: unescaped & which should be written as &
Cause:
The ampersand ("&") is a special character in HTML. It marks the beginning of a entity, like " " for a non-breaking space.
In XHTML, a entity must also end with a semicolon (";"). For example " "
Because this is so, any time a literal ampersand appears in a document, it needs to be written as a character entity, "&". Ampersands commonly appear in the query string of a URL, and need to be expressed as an entity there.
Example - Normal Ampersand:
 | Smith & son |
 | Smith & son |
Example - Ampersand in a Query String:
 | <a href="http://www.domain.com/cgi?x=1&y=2">query string</a> |
 | <a href="http://www.domain.com/cgi?x=1&y=2">query string</a> |
Solution:
Please replace "&" with "&".
References: