I have two MacBook Pros, running 10.5 and 10.8 . The new one running 10.8 contains an iCal that, after having been started off fresh, now contains several months of calendar items. Now I need to merge in the iCal database exported from my old 10.5 machine. I have backed up iCal on both machines, producing an .icbu database export file for each, plus .ics files for each individual calendar in both databases. If I import the old .icbu file into the new machine, it replaces all of my calendars and history with the old. Now if I try to import any of the .ics files I just exported from the new database, I get "Calendar can't read this calendar" from the same installation of iCal that just produced them! Apparently I'm stuck with either the old database or the new database, with no ability to combine the two. I can't believe that Apple left out such a critical capability - what am I doing wrong?