Why do I get a '"Calendar Cache" couldn't be moved' error when launching Calendar?
If repairing permissions with Disk Utility and/or checking permissions for the actual calendar-files in /Users/&lt;username&gt;/Library/Calendars do not work maybe this will:

https://discussions.apple.com/thread/3773022?start=0&amp;tstart=0

Seems a bit drastic though. I have not tried this myself. I suggest having a backup just in case.

Update: I just tried the instructions from the thread at apple discussions, and everything on my 10.8 system is OK. It's kind of a supercharged permissions-repair (lacking better terms atm).

If it works, thank macjack at the appe forums. If not, tell me :)

On my mac the ~/Library/Calendars/Calendar Cache is owned by me:
-rw-r--r--@  1 nils  staff  2813952 Jul 31 18:44 Calendar Cache

It may be of help if you post the output from this terminal command:
ls -lar ~/Library/Calendars/|grep "Calendar Cache"