Call external javascript

Hi,
I want to make to selected gridview row highlighted. But i'm keep getting "Microsoft JScript runtime error: 'ChangeRowColor' is undefined" error once i click on my gridview.
Putting my javascript together with html page was ok. Why cannot work in external js??

Please help!

My external js

var PreviousRow;



       function ChangeRowColor(Row, Index) {

           //If last clicked row and the current clicked row are same

           if (PreviousRow == Row)

               return;
               //do nothing

           //If there is row clicked earlier

           else if (PreviousRow != null)

               //change the color of the previous row back to white

               document.getElementById(PreviousRow).style.backgroundColor = "#ffffff";

               //change the color of the current row to light gray

               document.getElementById(Row).style.backgroundColor = "lightgrey";

               //assign the current row id to the previous row id

               //for next row to be clicked

               PreviousRow = Row;
       }

My HTML

<asp:GridView ID="GridView1" runat="server" AllowSorting="True"
            OnSorting="GridView1_Sorting" PageSize="20"
            OnPageIndexChanging="GridView1_PageIndexChanging"
            OnRowDataBound ="GridView1_RowDataBound"
            OnRowCreated = "GridView1_RowCreated"
            AllowPaging="True">

        </asp:GridView>
<script language="JavaScript" type="text/javascript" src="../Javascript.js"></script>  

My Code

protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e)
       {

e.Row.Attributes.Add("onclick", "javascript:ChangeRowColor('" + rowID + "','null')");
}

Tags: C#, ASP.NET