"By looking at this site I was able to find the location where the Outlook VBA project data is stored:
Outlook 2007 File Locations
I saw that there was already a project file (VbaProject.otm) in the directory despite the fact that none of the project contents were showing in Outlook. (Perhaps the file was corrupt.) I deleted the bad file and re-imported my macro code from a backup. I was then able to save the VBA project without any trouble."