'Application cannot be started' running SQL Server Reporting Services Report Builder

SQL Server Reporting Services delivers its Report Builder as a click-once application when you click on the 'Report Builder' icon in the toolbar of the web application, unfortunately sometimes it "burps" and throws out the error message "Cannot Start Application: Application cannot be started. Contact the application vendor." clicking on the Details... button which pops up a copy of the diagnostics in notepad. The key bit in the scenario I've seen is this:

ERROR DETAILS
	Following errors were detected during this operation.
	* [20/09/2018 12:57:30] System.Deployment.Application.DeploymentException (Subscription)
		- Unable to install this application because an application with the same identity is already installed. To install this application, either modify the manifest version for this application or uninstall the preexisting application.

This means that you've got multiple SSRS servers and the first time you ran/installed Report Builder was from a server other than the one you're now trying to open it from.

There are a couple of choice now:

1. Work out which server you first ran it from and run it from there - it is possible to connect to other servers once the app is open
2. Blow away the contents of C:\Users\[YourProfileNameHere]\AppData\Local\Apps\2.0 - this will toast all downloaded apps and I'm not sure just how supported this is
3. Download and install Report Builder as a "proper" app rather than a ClickOnce one - the SQL Server 2012 version can be downloaded from microsoft.com.

I've opted for option 3 and I probably wouldn't elect to go for option 2 unless everything else failed as there's a reasonable chance that there's related state stored elsewhere which could get out of synch.