"Failed to create a service in configuration file"

You may encounter this error message when you try to add a WCF base service to your web service project. The additional text of this error message is: A child element named 'service' with same key already exists at the same configuration scope. Collection elements must be unique within the same configuration scope (e.g. the same application.config file). Duplicate key value: 'FooProject.BarService'. The cause for this error message might be that you added a service to your project with the same name previously, then deleted it again. The remnants of that deleted service prevent the new service with the same name to be created. To resolve the problem do this:

1. In the web.config file locate the XML node within the node . For instance in the above example locate the node that describes the 'BarService'. Delete that node but leave in the file.
2. In the same file locate the node with an attribute 'behaviorConfiguration' and an attribute value of 'BarService'. This node also contains the endpoints for the service. Remove this node.
3. Try again, and this time it should work.

This is not a major problem but shows that a wizard for adding a service isn't necessarily coupled with an according wizard to remove the service in case you changed your mind. Removing means deleting the BarService.svc and its implementation file, e.g. BarService.svc.cs. It doesn't, however, delete the related entries from the web.config file.