Crystal Reports :: Paging Error - No Valid Report Source Is Available?

i have a load report on asp page

i have load report on button click

but when i click on next navigation button 

then it gives me error with popup

"No valid report source is available."

my code is:

protected void Button1_Click(object sender, EventArgs e) { GetData();
}
private void GetData() {
SqlConnection connection = new SqlConnection(strcon); SqlCommand command = new SqlCommand("Select * from demoforreport WHERE role='" + TextBox1.Text + "'", connection); SqlDataAdapter adapter = new SqlDataAdapter(command); DataSet dataset = new DataSet(); adapter.Fill(dataset, "demoforreport"); ReportDocument CustomerReport = new ReportDocument(); CustomerReport.Load(Server.MapPath("CrystalReport.rpt")); CustomerReport.SetDataSource(dataset.Tables["demoforreport"]); CrystalReportViewer1.ReportSource = CustomerReport; CrystalReportViewer1.DataBind(); }