checkbox.js

// To disable and clear the checkbox, use "prop" NOT "attr"
$("#FollowUp").prop("disabled", checked);
$("#FollowUp").prop("checked", false);

// Options for setting values
checkbox.val("disabled", false);  // Sets the value, but not if it is checked
checkbox.prop("disabled", false); // Disables the checkbox
checkbox.attr("disabled", false); // Also disables depending on version
checkbox.is(":checked");          // Returns checked value