Ответ перенаправить новую вкладку
Response.Write("<script>window.open('" + URL + "','_blank');</script>");
Mingles444
Response.Write("<script>window.open('" + URL + "','_blank');</script>");
protected void btnSave_Click(object sender, EventArgs e)
{
...//some code to insert records
Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "openModal", "window.open('NewQuote.aspx?val= " + this.txtQuotationNo.Text + "' ,'_blank');", true);
}