This error can appear during a project build in Visual Studio if you decide to create a stand alone installer when the project was initially set to use ClickOnce technology. The error message can occur when the signing certificate (.pfx) is deleted or the project is moved to another computer.
To prevent this message from displaying, right click on the project and select Properties. Click on the Signing tab and you will see the Sign the ClickOnce manifests checkbox selected. Remove the check here and then you can re-build the project without errors.