Custom 404 error page not working on IIS 8.5 - iis

Question

I have recently moved host and have had to set up Customer Errors again in IIS.
I can go to IIS Admin and Error Pages as follows:
Then I can go to the Custom Errors, and have set up the options as follows:
That creates my web.config file as follows:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<httpErrors errorMode="DetailedLocalOnly" defaultResponseMode="ExecuteURL">
<remove statusCode="500" subStatusCode="100" />
<remove statusCode="500" subStatusCode="-1" />
<remove statusCode="404" subStatusCode="-1" />
<error statusCode="404" prefixLanguageFilePath="" path="/error_404.asp" responseMode="ExecuteURL" />
<error statusCode="500" prefixLanguageFilePath="" path="/error_500.asp" responseMode="ExecuteURL" />
<error statusCode="500" subStatusCode="100" path="/error_500.asp" responseMode="ExecuteURL" />
</httpErrors>
</system.webServer>
</configuration>
When I test the pages, the 505 error works fine, and redirects to the right page, but the 404 doesn't redirect and returns the standard IIS 404 error. I have confirmed that the 404 error page is in place on the server in the correct location.
I can't see what else I need to do.

Answer 1

Got it working in the end (helped by finding this: http://forums.iis.net/t/1173965.aspx), using:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<httpErrors errorMode="Custom" defaultResponseMode="ExecuteURL">
<remove statusCode="500" subStatusCode="100" />
<remove statusCode="500" subStatusCode="-1" />
<remove statusCode="404" subStatusCode="-1" />
<error statusCode="404" path="/error_404.asp" responseMode="ExecuteURL" />
<error statusCode="500" prefixLanguageFilePath="" path="/error_500.asp" responseMode="ExecuteURL" />
<error statusCode="500" subStatusCode="100" path="/error_500.asp" responseMode="ExecuteURL" />
</httpErrors>
</system.webServer>
</configuration>

Answer 2

I was having a similar problem where I have a custom 404 page at /Error/Missing but it wasn't showing up for static files that didn't exist or for folders/directories that DID exist (but shouldn't be served by MVC). The controller for Missing page has the following:
Response.AddHeader("Content-Type","text/html; charset=utf-8");
Response.TrySkipIisCustomErrors = true;
Response.StatusCode = (int)HttpStatusCode.NotFound; // 404
Also I wasn't getting my custom error page if I returned the following in a controller:
return HttpNotFound();
I could change the IIS default errors to a blank page if I set PassThrough:
<httpErrors existingResponse="PassThrough" />
Changing it to "Replace" made the default IIS errors show again.
I also had a section in my web.config, but I've taken it out as I'm IIS 8.5 it doesn't look like it's needed any more.
<system.web>
<customErrors mode="Off">
</system.web>
So basically I couldn't get rid of default IIS messages - either one-liner or the more detailed ones. My httpErrors section looked like this:
<httpErrors errorMode="Custom" defaultResponseMode="ExecuteURL">
<remove statusCode="404" />
<error statusCode="404" path="/Error/Missing" />
</httpErrors>
Finally I came across this question and I was looking at the other answer on this question and realised that I could try a ResponseMode on each error line. I thought that wouldn't be necessary as I had the defaultResponseMode set - but it makes a difference!!
So, if you want to serve up a custom 404 page use this httpErrors module:
<httpErrors errorMode="Custom">
<remove statusCode="404" />
<error statusCode="404" path="/Error/Missing" responseMode="ExecuteURL" />
</httpErrors>
I've put all these details here so this hopefully shows up for someone else searching the same things I did - hope it helps!