Problem with readString.indexOf

Hi all, about four months ago i wrote a code in order to turn on or turn off some leds with Fishino uno (a simple Arduino with wifi, rtc and sd integrated). I'm trying it now but the IDE tells me that readString.indexOf is not declared in this scope.
The part of the code is this:

client.println("<h2>LED 1</h2>");
        client.print("<h2><a href='/?L=1'>ON</a> | <a href='/?L=0'>OFF</a></h2>");
        client.println("
");
        client.print("<span>LED 1 STATE : </span>");
          if (readString.indexOf("L=1") > 0) {
          	client.println("<span style='color:green'>ON</span>");
          digitalWrite (led1, HIGH);
            }
           if (readString.indexOf("L=0") > 0)
            {
          	client.println("<span style='color:red'>OFF</span>");
          digitalWrite (led1, LOW);
          }

How can i replace this part of code?

How can i replace this part of code?

I use copy/paste. Otherwise read the below on the best way to get help from the forum.

http://forum.arduino.cc/index.php/topic,148850.0.html