[VE][25] Validator Picks Out PHP Variables in Link URL

Validating http://rhe.pehjota.com/
Error [25]: "general entity X not defined and no default entity"


I tried to validate my page for XHTML 1.0 Strict, but the validator picked out a PHP variable in one of my links (a link to a PHP file with variables defined in the URL) and said the variable was undefined, possibly due to and "undefined entity reference" or an "unencoded ampersand."