Should you want to go ahead and delete a project, there are a number of reasons a project or sub-project cannot be deleted:
- There are to-do's or sub-projects created underneath it
- There are invoices associated with it
- Invoice planning has been created for it
- Hours are logged to it
- Expenses are logged to it
- Special rates have been applied to it
If any of these is true, you'll first have to remove those before you'll be able to permanently remove the project/sub-project.