When working with ActiveReport in a MVC application, you may occasionally receive either of the errors.
Common reason for both the errors relate to incorrect mapping of IIS Handlers. The following sections from the documentation show how you can configure the different version of IIS for ActiveReports. Configure Handlers for IIS 6.0 Configure Handlers for IIS 7.0 In case you continue to receive the error, you can verify whether the error is occurring due to incorrect handler mapping for IIS or is there any problem the way your application has been designed to access the reports internally. This can be easily confirmed using the Internal Development Server integrated with Visual Studio. When you run a file-system Web project in Visual Studio, you can specify the Web server that Visual Studio uses to run (test) the application. You can choose from the following Web servers:
In our scenario, we have to select the Visual Studio Development Server. Following steps show how you can configure the Visual Studio to enable the internal development server for hosting the web application.
If the Project compiles and shows the report, this confirms that the actual issue remains with the handler mappings which need to be corrected. To read and know more on the various server options available with in Visual Studio, you can visit this link from MSDN.