使用两列过滤一个关键字的结果时出错

当我添加另一列(ReplyN)到过滤器时，我得到一个错误这是我的代码

if($keyword) {
            $filter .= "'n $syntax t.title LIKE .$db->Quote("%$keyword%") OR t.ReplyN LIKE ".$db->Quote("%$keyword%");
            $syntax = "AND";
        }

完整代码为:

// Setup query filter
        if($keyword) {
            $filter .= "'n $syntax t.title LIKE .$db->Quote("%$keyword%") OR t.ReplyN LIKE ".$db->Quote("%$keyword%");
            $syntax = "AND";
        }
        if($ms > 0) {
            $filter .= "'n $syntax(t.milestone = $ms)";
            $syntax = "AND";
        }
        if($status == 1) {
            $filter .= "'n $syntax(t.progress < 100)";
            $syntax = "AND";
        }
        if($status == 2) {
            $filter .= "'n $syntax(t.progress = 100)";
            $syntax = "AND";
        }
        if($priority > 0) {
            $filter .= "'n $syntax(t.priority = $priority)";
            $syntax = "AND";
        }
        if($assigned == 2) {
            $user = PFuser::GetInstance();
            $filter .= "'n $syntax (tu.user_id = ".$user->GetId()." AND tu.task_id = t.id)";
            $syntax = "AND";
        }
        if($assigned > 2) {
            $filter .= "'n $syntax (tu.user_id = ".$assigned." AND tu.task_id = t.id)";
            $syntax = "AND";
        }
        if($all) {
            $filter .= "'n $syntax(t.project IN($project))";
        }
        else {
            $filter .= "'n $syntax(t.project = '$project')";
        }