You might have added an assembly or a manifest file as a content file. You should use the Add Reference command instead of Add File so that the dependent assembly is properly referenced by the project system. More sophisticated projects commonly mark the .exe.manifest in the bin folder as a project file, but you should avoid doing so. The hidden app.manifest file becomes the .exe.manifest file and can be edited manually for advanced scenarios>Yes, the link showed only what the problem was and not how to fix it.