Currently Being ModeratedMar 1, 2013 12:01 PM (in response to ronenhaim)
Have you verified that you can restore your library from the Dropbox servers and it will be in good working condition? Synicng to Dropbox may not create a good backup when it's copied back to your Mac if needed at some time.
Try the folloiwng: launch iPhoto with the Option key held down and in the window that comes up select the iPhoto library that resides in your local Dropbox folder. Run it there for a while and then retrieve the library from Dropbox to a different location and open it to see if it is a good, working library. If so then keep using the library in the local Dropbox folderl and get rid of the one in your Pictures folder.
HOWEVER, the media browser in other application may not work since the library is not in its default location. To try to correct this you can create a symbolic link to the library in the Dropbox folder and place it into your Pictures folder. You may have to remove the symlink at the end of the file name so its file name is the same as the iPhoto library.
If the retrieved copy of the library does not worn then you should use a different backup scheme, like an external HD and Time Machine.
Also don't try to use the same library on another Mac thru Dropbox. That's a sure fire disaster.