Umbraco 404 custom error page not working on staging/production server

My custom 404 error page in Umbraco was working locally but not when I deployed to staging/production. The reason was explained very nicely here: StackOverflow.

So basically you can add the following to your deployed web.config under :

Umbraco bug with deleting data types

In Umbraco v4.0.3 I needed to delete a data type I created. Once the data type had been deleted I tried modifying the document type which had a property using the deleted data type, and an error occurred:

Node node exists with id '1609'.

After a lot of searching it seems Umbraco did not delete a record in cmsPropertyType with the dataTypeId = 1609 - the data type I deleted. After deleting this record I could modify the document type without getting an error.

App_Code Class not working

I have a class in my App_Code folder and I am trying to reference it in my code behind. The name spaces are the same but I keep getting an error that is can't find the class.

The reason being I am using a web application project and not a web site project. In order for the class to be recognised I need to change the "Build Action" of the class file to "Complie" from "Content".

Build and it works now.