Parameterization issue in Truclinet script

Hello,

I am trying to use the parameter value inside the for loop, but the value is not taking in the same way as expected.   I am giving unique, each occurance in the paramater file.  When the loop starts executing it takes only the first two values.   Then i tried to use advance param inside the loop to force it to go to next value but it still doesnt take new value.  Request anyone to provide me solution.

Code:

truclient_step("50.1", "For ( var i = 0 ; i < 10 ; i++ )", "snapshot=Action_50.1.inf");
        {
            truclient_step("50.1.1", "Evaluate JavaScript code var a = LR.getParam('p_S...window.alert(a);", "snapshot=Action_50.1.1.inf");
            truclient_step("50.1.2", "Click on 21385 854 8 checkbox", "snapshot=Action_50.1.2.inf");
            truclient_step("50.1.3", "Evaluate JavaScript code var b = LR.getParam('p_P...window.alert(b);", "snapshot=Action_50.1.3.inf");
            truclient_step("50.1.4", "Click on Perf Product 15P 1B 004 checkbox", "snapshot=Action_50.1.4.inf");
            truclient_step("50.1.5", "Execute TC.advanceParam ( 'p_S' )", "snapshot=Action_50.1.5.inf");
            truclient_step("50.1.6", "Execute TC.advanceParam ( 'p_Pn' )", "snapshot=Action_50.1.6.inf");
        }