Aperture Library will not Import
This seems to be an issue with the latest release of Aperture and has been documented in the Aperture Discussion Forums.
In my case I was able to resolve it by creating a project on the desktop Aperture Library containing a dummy image that was also on the laptop Aperture Library project and exporting the modified project as a new library. Then importing the new library containing the project to the desktop. This time the "merge" / "add" dialogue box appeared and I was able to successfully bring the new project into the desktop library.