When trying out the new Blazor project type in Visual Studio 2019 I encountered this error:

There was an unhandled exception on the current circuit, so this circuit will be terminated. For more details turn on detailed exceptions in ‘CircuitOptions.DetailedErrors’.

It turns out I was simply missing a service reference in the Startup.cs file.

The page I was trying to navigate to was one I had created by copying and modifying the “Weather Forecast” page that comes with the default Blazor template you get out of the box when you create a new Blazor project.
In this page a service and model from the ‘Data’ folder are used to simulate retrieving data from a source and delivering it to the page:

Adding the missing reference to the startup file fixed the issue. No more “unhandled exception on the current circuit” error when navigating to the new page 🙂