Javascript error

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ASP.NET

Hi,

I have done gridview edit control program.
Output is displayed but when I am clicking on the edit button it is showing javascript error.

Can I know what might be the problem?

the error is:_dopostback('gridview','edit$')
provindiong the code below:

<form id="form1" runat="server">
    <div>

    </div>
    <asp:GridView ID="GridView1" runat="server" AutoGenerateEditButton="True"
        onrowediting="GridView1_RowEditing">
        <Columns>
        <asp:CommandField ShowEditButton="true" />
        <asp:BoundField  HeaderText="EMPID" DataField="emp_id" />
        <asp:BoundField  HeaderText="EMPNAME" DataField="emp_name" />
        <asp:BoundField  HeaderText="EMPSALARY" DataField="salary" />

        </Columns>

    </asp:GridView>
    </form>

public partial class _Default : System.Web.UI.Page
{
    DataSet ds = new DataSet();
    protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection conn = new SqlConnection("Data source=10.0.2.8; user id=sa; password=change_123; database=sample");
        conn.Open();
        SqlDataAdapter da = new SqlDataAdapter("select * from emp", conn);
        DataSet ds = new DataSet();
        da.Fill(ds, "emp");
        if (IsPostBack==false)
        {
            GridView1.DataSource = ds.Tables[0];
            GridView1.DataBind();
        }
    }
    
    protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        GridView1.EditIndex = e.NewEditIndex;
        GridView1.DataSource = ds.Tables[0];
        GridView1.DataBind();
    }
}

Thanks in advance