Merging calenders on 10.8.2

Before I updated to OS X (10.8.2) and iCloud is used to be able to merge 2 calenders within iCal

First I would export a calender as at .ics file

Then I would import the .ics file and select another calender to import it to.

This would achieve the merge.

However now having updated to 10.8.2 and iCloud I get this window pop up upon following the above process.

This message has to be if I click ignore or try again it just comes back or if I click revert to server an entry for that calender will delete. However my calenders have loads of entrys on them and each one has to be clicked away which is a long and slow process.

Is it still possible to merge calenders as I would like to merge some of my older calenders?