Try the steps in the following except for the locking of the faces db file.
Disable_Faces
1 - open the library like this in the Finder.
2 - in the Database folder move this file to the Trash: Faces.db.
3 - close the package/folder and launch iPhoto. Close it after a moment.
4 - while viewing the contents of the package type Command+F to start a search.
5 - set the criteria of the search to: Kind is Image and Name Contains "face".
6 - select all of the files in the search results window and drag to the Trash.
7 -close the package and launch iPhoto.
This will remove any "faces" images in the library as well as setting the faces database back to the beginning, empty.
Of course make a temp, backup copy of the library before trying this.