Sounds like just a permission error. Fixing permissions won't fix it since it isn't considered "system files" so I'm going to guess that if you went to your iPhoto library and hit Command (Apple) + I it will say something other than "You can: Read and Write" under permissions.
I'm assuming you are using a Admin account as I continue with this...
Get BatChmod (
http://macchampion.com/arbysoft/)
Click "File..." in BatChmod and navigate to your iPhoto Library.
Change Owner to your user name if it isn't already and select all the boxes below it. (they stand for Read, Write and Execute)
If any other users will be accessing the the iPhoto Library, change group to the appropriate group. If there is no group that contains all users who need to access it, I recommend you just select "admin" and check all the boxes and then check all the boxes for other. If there is a group that encompasses all the users needed (if you know how to make one, go ahead, but I'm not providing instructions) select that group and select all the boxes. For other, in this case, I recommend that you either select Read only or none at all.
Under "Enclosed Files and Folders" select both checkboxes.
Click "Apply"
This should work, but as you start up iPhoto, hold down the option (alt) key and select "Find Library..." and navigate to your iPhoto Library.
I hope this helps. If it still doesn't work, you'll need to re-import everything... I've had a lot of problems with iPhoto before.
EDIT:
I posted this before I saw your 3rd post. The numbered folders go like this (or should):
iPhoto Library/yyyy/mm/dd
They have nothing with how your photos were organized in iPhoto. AlbumData.xml contains all of that information.