1. Open both projects within the same session of Revit.
2. Place the keynote schedule on a sheet.
3. Select it, and hit Ctrl-C.
4. Open a sheet in the other project, the one you want to copy it into.
5. Hit Ctrl-V & click where you want to paste it onto a sheet.
Now it will be a proper schedule within your project. For whatever reason, you can only cut-and-paste schedules from a sheet to another sheet between projects.