<label><input id="GRP010" type="RADIO" value ="900">Radio button</label>
    <input id="AF92" maxlength="254" size="15" name="AF92">

$(document).ready(function(){

    var value2 = $('input:radio[name="GRP010"]').val();
    var checked2 = $('input:radio[name="GRP010"]').is(':checked');

    if (checked2 == true && value2 == '900') {
        $("#AF92").attr("enabled", "enabled");
    } else {
        $("#AF92").attr("disabled", "disabled");
    }
});

$("#AF92").attr("disabled","disabled"); // will disable
$("#AF92").removeAttr("disabled"); // to enable

$('#GRP010').on('change', function(){
var checked = this.checked;

    if(checked && value2 == '900')
        $("#AF92").removeAttr("disabled");
    else
        $("#AF92").attr("disabled","disabled");
})

$(document).ready(function(){
    var value2 = $("#GRP010").val();
    var checked2 = $("#GRP010").is(':checked');

if (checked2 == true && value2 == '900')
   {
     $("#AF92").attr('readonly', false);
   }
else {
        $("#AF92").attr('readonly', true);

    }

});

$("#AF92").removeAttr("disabled")

$(".radioclass").click(function(){
    if ($('#GRP010').val()) { //you actually don't need double check
        $("#AF92").removeAttr("disabled");
    } else {
       $("#AF92").attr("disabled",true);
    }
});

$("#GRP010").bind('change', handler);

function handler(){
  var value2 = $('input:radio[name="GRP010"]').val();
        var checked2 = $('input:radio[name="GRP010"]').is(':checked');

 if (checked2 == true && value2 == '900')
       {
         $("#AF92").attr("enabled","enabled");
       }
 else {
            $("#AF92").removeAttr("disabled");

        }

}

$(function(){
    var radio = $('#GRP010'),
        txtInput = $('#AF92');

    var changeState = function()
    {
        txtInput.prop("disabled", radio.is(':checked') && radio.val() == '900');
    };
    changeState ();

    radio.change(changeState);
});

<label><input id="GRP010" type="checkbox" value ="900">CheckBox</label>
<input id="AF92" maxlength="254" size="15" name="AF92">

$(document).ready(function(){
    $('#GRP010').on('change', function(){
        if($('#GRP010').is(':checked') && $('#GRP010').val()== '900')
            $("#AF92").removeAttr("disabled");
        else
            $("#AF92").attr("disabled","disabled");
    });
});