FindControl in user method

Hi,
    Is it possible to use FindControl to reference a DropDownList on a GridView from a user method? The first line of the below code works fine for a FormView but fails for a GridView.
Thanks
Paul.
 
private void ClientE(string AClient) //Gets Project Number List for Selected Client
    {
        DropDownList ProjectNumberDDL = (DropDownList)GridView1.FindControl("ddlProjectNumberE");
        System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection();
        System.Data.SqlClient.SqlCommand command = new System.Data.SqlClient.SqlCommand();
        System.Data.SqlClient.SqlDataReader myDataReader = null;
        conn.ConnectionString = ConfigurationManager.Con ...