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Editorial Team
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Asked: 2026-06-14T22:16:25+00:00

Using: Visual Studio 2010 with ASP.net 4.0 I have a website which uses URL

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Using: Visual Studio 2010 with ASP.net 4.0

I have a website which uses URL rewriting and I want to keep the rewritten URL on Postback. I’ve read a lot of the topics on this subject and I still haven’t been able to figure out if this is possible.

For example:

http://localhost/ActualPage.aspx?PageID=4

Is rewritten as:

http://localhost/member/forum.aspx

The page contains a number of controls which use a Postback (for example a Telerik RadGrid with sorting and paging). Normally when the postback takes place the browser is redirected to the unrewritten url – the address bar shows /ActualPage.aspx?PageID=4 etc. In this scenario everything works correctly.

However I want to retain the rewritten URL after the postback, so I have coded to change the Form.Action property to be the rewritten URL like so:

Page.Form.Action = "/member/forum.aspx"

Now the page correctly retains the URL in the address bar but throws a "Validation of viewstate MAC failed" error when the postback occurs – which I would expect it too as the viewstate originated from a different URL.

Strangely this problem occurs even when enableViewStateMac is set to false (either in the page or in the web.config) – but I don’t want to disable this anyway.

Effectively I think what I need to do is tell the page / viewstate mac authorisation that is it ok to accept input from this alternative URL but I can’t find anyway of doing this. I’ve tried different URL rewrite system to see if that makes a difference, and i’ve tried added a generated machineKey – neither of which has made any difference. Is there any way of doing this?

In short I want:

  • Rewritten page with postback going to the rewritten URL
  • ViewStateMac enabled
  • No viewstate validation errors

I remember in earlier versions of .NET using a .browser file with FormRewriterControlAdapter but this doesn’t seem to make any difference in .NET 4 (I don’t remember if it successfully retained the URL anyway).

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1 Answer

  1. Editorial Team

    I have found a solution – it turns out the problem was actually unrelated and masking itself as a ViewStateMac issue.

    Previously I had been redirecting all the URLs to one page, doing a database lookup and then using Server.Transfer() to deliver the correct page to the browser. The real problem was being caused by using Server.Transfer() – which it seems is recognised by Microsoft to be an issue when working with the viewstate.

    I have made adjustments so IIS performs the database lookup, the entire rewrite and therefore Server.Transfer() is not used – and the original problem I had has been resolved.

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