IIS custom errors not showing custom error page

asp.net, iis-7

Solution

After further research I see that this means that IIS is displaying the error rather than ASP.NET.

I changed the system.webServer part of my web.config so IIS can also use the custom error page and that has solved the problem.

<system.webServer>
  <httpErrors errorMode="Custom" existingResponse="Replace">
    <remove statusCode="500" subStatusCode="-1" />
    <error statusCode="500" subStatusCode="-1" responseMode="ExecuteURL" path="/500.aspx" />
  </httpErrors>

Problem

I have custom error pages setup on an ASP.NET website. There is one error that is not showing a custom error page, and just showing the usual yellow ASP.NET error page. If custom errors are turned on it shows "Server error in / application" / "Runtime error", but if custom errors are off it shows "validation of viewstate mac failed" error. The relevant parts of my web.config are: ``` <system.web> <compilation debug="false" targetFramework="4.0" /> <customErrors mode="On" redirectMode="ResponseRewrite"> <error statusCode="404" redirect="/404.aspx" /> <error statusCode="500" redirect="/500.aspx" /> </customErrors> <system.webServer> <httpErrors errorMode="DetailedLocalOnly" /> ``` To trap for this error do I have to use a different status code or substatuscode or is there something else? NB. Server 2008 R2, IIS 7.

Original source