Question: getting an error when trying to make a project complete from Edit Project lightbox or from update stab.
Answer: Please check that you do not have any task or issue in not Complete status or in a Pending approval status. You can add a View with "Status" column for both Task and Issue lists to check this option. http://screencast.com/t/CYJbyw590sB
You must approve/close them and then be able to mark the whole Project as Complete.