SYMPTOMS
A project has been created in error and on the next day a user tried to delete the project. But there is an error message saying that the project cannot be deleted because it is part of a portfolio.
RESOLUTION
As the project was automatically added to a project, it means there is probably a portfolio of type 'All active projects' that auto-updates the project it contains. In that case, please change the project to be deleted to completed status. On the next day, it will be removed from the 'All active projects' portfolio and can be deleted.