Local web.config custom errors setting is ignored?

I recently changed my machine and had to reinstall VS 2010. Now, every time I build a project I get this error page, although I have set the mode='Off' for custom errors. Seems as if the local web.config is ignored or something.

Thanks.

Runtime Error Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine. Details: To enable the details of this specific error message to be viewable on remote machines, plea ...