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Failed to map the path '/' exception


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Report Viewer ASP.NET WebForms

This article relates to the Legacy ASP.NET Report Viewer.


When trying to show a report in our web ReportViewer control, Visual Studio throws the exception from below.

Error Message

InvalidOperationException: Failed to map the path '/' 


The exception is raised by the WebConfigurationManager class and if we try the following:

Configuration cfg =  WebConfigurationManager.OpenWebConfiguration(System.Web.Hosting.HostingEnvironment.ApplicationVirtualPath);   

In the Page_Load method, it would cause the same error, which excludes the possibility of this being an issue with the web viewer.

The error is related to the built-in VS web server Cassini - the issue proved to be not running VS as Administrator. In Vista and Win 7, warning messages are displayed when Visual Studio is not being run as administrator.


There is a tick to "silence" this warning. This way, if Visual Studio is not set to run as administrator, by default, or is not started as administrator explicitly through the context menu "Run as Administrator", there are good chances you'll get the Failed to map the path '/'. exception.

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