Problem opening iPhoto files

Question

We have five user accounts on our machine. I took all of the separate iPhoto libraries and combined them into a single library under the Users/Shared folder. Everything worked great for a couple of weeks, but now I'm getting the "An error occurred while trying to save..." message everytime I open the file. No other accounts are logged on, just mine, the admin account. Hmmm....

Answer 1

I first moved my library (the admin) to the shared folder, I then moved each of the other libraries to the same folder and imported them one at a time into my library using iPhoto's File/Import to Library command. The combined iPhoto library is 30+ Gig. I then made a sparse bundle of 50 Gig to hold the combined file. I changed the Sharing and Permissions for this file to allow myself, staff, and everyone to read and write to the file. To access the photos, all we had to do was mount the sparse bundle and open the iPhoto application.
Everything worked great for about a week. All of the users could mount the sparse bundle image, start iPhoto, and upload photos, modify photos, and create albums. When finished, we unmount the disk so others could use the file. This was a great way to share photos without constantly swapping photos between accounts and creating duplicates.
The problem is that last night, when I mounted the disk and started iPhoto, I got an error message saying: "An error occurred while trying to save..." and telling me that my changes would be lost. I restored the large file from Time Machine from a few days ago when I know things were working. That didn't work. I reset the Sharing and Permissions back to just me being able to read and write. That didn't work. I am now going to rebuild the iPhoto database after starting the application while holding down the Alt & Command keys. If that doesn't work, I don't really know what to do next.
I am curious as to what would trigger this error. I would like to prevent it from happening again.