How to load second config

Hi,
Im working with .NET 4.0 and VS 2010 and a want to split my config into 2 seperate files, so that in the first one contains only the CMS specific configitems and in the second one the customer specific things like connectionstrings, appsettings and the additional user controls.
Now when I spilt those files I get all kind of runtime errors, he cannot find my connectionstring or extra controls that I have registered into the second config (customer specific).
Thx!
Wouter

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