<customErrors mode="RemoteOnly" defaultRedirect="~/errors/error.aspx">
<error statusCode="500" redirect="~/errors/error500.aspx" redirectMode="ResponseRewrite" />/>
</customErrors>
<asp:Label runat="server" ID="ErrorMessage"></asp:Label>
protected void Page_Load(object sender, EventArgs e)
{
var error = HttpContext.Current.Server.GetLastError();
this.ErrorMessage = error.Message;
}