Server.Transfer throws Error executing child request. How to resolve?

I was hooking into the request pipeline in the OnPreRequestHandlerExecute event, and found I couldn't use Server.Transfer because it threw the same error as yours about executing a child request.

Using HttpContext.Current.RewritePath didn't work because it seemed to be ignored and I wasn't redirected anywhere.

If you're using IIS 7 and up, you can use Server.TransferRequest instead which did the trick for me.

The differences between the two methods are covered in this answer: TransferRequest vs Transfer in ASP.Net

My fix was different:

An online query produced this Microsoft Knowledge Base article which stated the resolution would be to use Response.Redirect instead of Server.Transfer.

I changed the command and got a more accurate "404 Error Message" instead of the cryptic "Error executing child request" message.

That led me to inspect the redirect string and I noticed my path was off.

I fixed the Transfer String from "ErrorPage.aspx" to "../ErrorPage.aspx" (notice the path change) and Server.Transfer worked just fine.

I found an alternative to Server.Transfer()

I used

 HttpContext.Current.RewritePath("somefile.aspx");

This solved the issue.

If you happen to see this exception occur in the VS.NET IDE during debug, go ahead at least once and press F5 to continue debugging. In my case, the actual page did render with the ASP.NET exception that was really causing the issue. In my case I had an incorrectly formatted asp:ChangePassword control that was actually causing the "Error executing child request" exception.