Can't run without setting a Startup Project first

You must set a startup project before running. This error has the following causes and solutions:

• You had a startup project and two or more other projects in the project group that could be a startup project, but you removed the one that was a startup project.

  Make one of the projects a startup project by right clicking the project in the Project Explorer and selecting the Set as Start Up menu item.

• This error also occurs in any other case where there is more than one project that could be a startup project after removing the current startup project.

  Make one of the projects a startup project by right clicking the project in the Project Explorer and selecting the Set as Start Up menu item.