How to import an old iPhoto 09 library to iPhoto 11?
Open the old library directly by holding down the [option] key while starting iPhoto. iPhoto will then allow you to browse to the library location (use the "Other Library" button) and should update it automatically to iPhoto '11 format. You may want to back it up first

Close iPhoto and restart holding [option] once again, make sure the active library is your current (new) one. Try reimporting the old library now. It might still be greyed out in the file picker but double click it anyway, it should import.