Why can't I no longer edit or make changes to my Archived Project(s)?
A new feature request was implemented that closes a project that has been archived which results in a user being unable to be edit the project or have time added to the project.
A PMO manager or Project Manager on the project can Open the project by clicking on the project and if you hover the Edit icon you will see an option to Open/Un-Archive project.
This will allow the project to have changes made to it and once your done, you can just select to Archive the project again.
An alternative option is to not restrict changes from projects and tasks after closing/archiving a project by a System Administrator. In the left navigation they can go to "Administration -> Projects -> Settings.
On this page a System Administrator can select to enable the option "Enable changes to the project and tasks after clsoing/archiving a project".