User1713851783 posted
There are a lot of ways to pass data from a page to another; for a comprehensive coverage look at
Transferring Data Between ASP.NET Web Pages.
In your case I think that the best solution could be session variables. In the page with the form, if IsPost is successful, you should place this snippet:
Session["message"] = validationMessage;
Response.Redirect("yourDestinationPage");
and in yourDestinationPage something like:
@if(!string.IsNullOrEmpty((string)Session["message"])){
<p>@Session["message"]</p>
}