Question: Why can I not change the Status of my Project from Complete back to Current?
The cause of this problem is the "Completion Mode" setting on your Project. If a Project's "Completion Mode" is set to Automatic, then the Project will automatically change the Status from "Current" to "Complete" once the Project's "Percent Complete" bar is 100%. If a Project's "Completion Mode" is set to Manual, then the Project Status can be changed from Current to Complete anytime.
You can change this by navigating to "Edit Project" and scroll down to "Completion Mode." Once you are there, change "Completion Mode" from "Automatic" to "Manual."