Todd,

Scary stuff, but hopefully easily fixable.

First thing’s first — back up your existing libraries! Before you do any repair work, let’s make sure that you have those libraries in an untouched state backed up to return to at any time. Do a Finder copy to another hard drive. Go buy one if you have to. Whenever entering a state of “I’ll try this, then this, then this…” I think it’s VERY GOOD IDEA to have your stuff backed up in its current state. You never know what clever “fix” you try could end up doing more harm than good—and you want a way back.

Now… can you tell us what the EXACT error is? What does it say, precisely?

The first repair to try is to simply hold down the command and option keys while launching Aperture, which will give you three repair options. Start with the first one (permissions) and see if that works. If not, try the 2nd then 3rd. If you’re not sure what library is being opened, you can hold down just option on launch and get the library chooser. This will also let you create a new, empty library just to be sure that Aperture will even run (probably a good idea to start, to eliminate other non-library specific problems).

Let’s take it from there.

-Joseph @ApertureExpert