This error is thrown if you double-click a crystal report in the Visual Studio Solution Explorer.
The error is caused by a failure in the solution project file (extension csproj).
Close your solution and the use the “Find in Files” option in Visual studio on your project folder. Search for .rpt
Below is an example;
<SubType>Designer</SubType> <==== Wrong entry
Remove the Subtype node and store the cproj file.
Open your solution and now you can open the Crystal Report directly by double-clicking the report in the solution explorer.