When finished with projects

Did you update that project from 10.0.9?

Yep, everything is updated.

Did you save the old version when they updated?

Darren Roark wrote: Did you save the old version when they updated?

No, I trashed it... I always save the old ones for some time. So it's been a while since I updated this drive.

Neguah wrote: So it's completely fine copying inside finder? No matter what files I want to copy?

That is not what Ben wrote. It is fine to copy Libraries in finder. It is not fine to use "Show package contents" and move around the items inside a library, i.e. projects and events.

As for your initial issue. When you move projects and events to a library you are asked if you want to include proxy and optimized media. If those check boxes aren't set you will not move the proxy files. If you don't remember to set your user interface to use Optimized or original media you will get the red "clip not found". In that case you can either re-generate proxy files in the new library or decide to use original media.

I checked include proxy media when I was asked. The optimized media was not checked as I did not work with optimized media. Only proxy.

Instead of "show package content", I just moved the whole package inside Finder to my backup drive. Is that not the correct way? It's working now, but will I encounter some problems later on?

Edit:
Ahhh, the package is the library. Damn I'm dumb...

I closed a library, but when I wanted to open it again I got this message: bildr.no/view/R2JYaDR5

In order to open it again, I have to close FCPX and open it again.
How do I open the library without closing FCPX?