the invalid=true querystring variable maens that alidation has failed.
try changing:
$WAFV_Errors .= WAValidateRQ((isset($_POST["fieldset_group_File_Picture_Upload"])?$_POST["fieldset_group_File_Picture_Upload"]["name"]:"") . "",false,6);
to:
$WAFV_Errors .= WAValidateRQ((isset($_FILES["fieldset_group_File_Picture_Upload"])?$_FILES["fieldset_group_File_Picture_Upload"]["name"]:"") . "",false,6);