You might have come across this error while working on a WCF project on Vista, IIS 7.0 with Visual Studio 2005. Actually Microsoft has tightened the security on VISTA and most of the time it is annoying when it asks your permission. Following is the detail error message I received while trying to run a WCF project, however I found a simple solution to fix it.
HTTP Error 500.19 - Internal Server Error
Description: The requested page cannot be accessed because the related configuration data for the page is invalid.
Error Code: 0x80070005
Module: IIS Web Core
Requested URL: http://localhost:80/ProductsService/ProductsService.svc
Physical Path: C:\Test\ProductsService\ProductsService\ProductsService.svc
Logon User: Not yet determined
Logon Method: Not yet determined
Handler: Not yet determined
Config Error: Cannot read configuration file
Config File: \\?\C:\Test\ProductsService\ProductsService\web.config
More Information...This error occurs when there is a problem reading the configuration file for the Web server or Web application. In some cases, the event logs may contain more information about what caused this error.
Server Version Information: Internet Information Services 7.0.
Solution: Compile the project and place the deployable files under C:\Inetpub\wwwroot\<projectname>. Make sure that the physical path of the respective Application (e.g. ProductsService in above error case) under IIS now points to new path.
It looks like that if you run your application under IIS 7 and the physical path of any application is other than wwwroot then it will give the above error message or you provide that folder some special permission so that IIS can access it.