Best answer as chosen by user Steve 1 2 3: I know the answer to this, but
by mrmacfixit - 8/4/11 4:54 AM
In Reply to: iPhoto library copied from old computer won't show by Steve 1 2 3
I have to remember where I found the solution.
One hesitates to ask why you did not move the Library using the Disk Migration tool, which would not have eliminated this problem but would have removed any variables that Drag and Drop may have introduced.
However, I will continue to rack by memory for the answer to the problem, I know it exists.
Meanwhile, make a backup copy of your iPhoto Library and move it to another location on the HD