The following exception occurs when you attempt to add a Html5 Report Viewer from the VS item template in a project that already contains a CLR report:

"Error: Fail to add project reference System.Runtime.InteropServices.COMException (0x80004005): Adding 'WebApplication2' as a project-to-project reference would cause this project to reference itself. at VSLangProj.References.AddProject(Project pProject) at Telerik.Reporting.Vs.Common.ProjectManager.TryAddProjectReference(Project projectToReference)"

The viewer is still added successfully and displays the report.