I got this issue with Visual Studio 2015 Enterprise Edition.
Every time I open a Dynamics NAV report layout in Visual Studio, RDLC is rendered as XML file instead of visual layout with all the fields and tool boxes.
How the report layout looks:
FIX : In order to fix the issue you need to install “Microsoft SQL Server Data Tools”.
To install “Microsoft SQL Server Data Tools” you need to go to
Control Panel -> Programs and Features – > Microsoft Visual Studio <Edition> -> Change
Or you can re run the installation setup.
From the features list, enable “Microsoft SQL Server Data Tools” option and proceed.