Add-in can't reference project

Projects are dynamic, but add-ins are static. This error has the following cause and solution:

• You tried to create an add-in from a project that references another project.

  The semantics of projects can change in a way that affects referencing projects and add-ins. Therefore, you can't create an add-in from a project that references projects.

For additional information, select the item in question and press F1 (in Windows) or HELP (on the Macintosh).