Unable to close dialog

Hi guys, I'm having a trouble closing a jquery dialog box, it gives me an error - Object doesn't support this property or method.
Here's my code loading a jquey dialog box.

[Code]
$(document).ready(function() {
            $("#btnLookUp").click(function() {
                $("#searchActor").dialog({
                    autoOpen: "false",
                    resizable: "false",
                    height: "350",
                    width: "320"
                });

                $("#searchActor").load("LookUp/ActorsList.aspx");
                $("#searchActor").dialog("open");
                return false;
            });
        });
[/code]

Using the function below, append whatever selected value on the dialog to the textbox
[code]
 function GetSelectedGrid(param) {
            $("#txtActorID").val(param);
            $("#searchActor").dialog("close");
        }
[/code]

However, the highlighted statement prompts the error - Object doesn't support this property or method.