Is it possible to display more than one error message for custom validator?

<asp:CustomValidator runat="server" id="cusCustom" controltovalidate="txtCustom" onservervalidate="cusCustom_ServerValidate" errormessage="Error message!" />

protected void cusCustom_ServerValidate(object sender, ServerValidateEventArgs e)
{
    if(//validatation is true)
        e.IsValid = true;
    else
        e.IsValid = false;
}