Aperture allows you to filter projects in the Library tab by substring. It also lets you search for a photo by name, and from the photo you can find the enclosing project.
However, if there’s a filter in Library that doesn’t match the container project, you’ll get an empty project. Kind of worrisome — you might think your Library is corrupted. Clear the Library filter and you’ll see the project.
It’s a bit of a minor bug really. Aperture should probably give an error message, like “clear Library filter to view project”.