I think I might have stumbled into the reason why this problem seem to pop up for all of us:
Poor programming from developers who haven't done their homework.
Whenever you have symbols or characters other than the common letters in the English alphabet, in the location name, I get this problem. Regardless of I get the invite through iCloud or Google Cal.
Example: If I get an invite with a "$" sign in it or an "é" in the location (like café).
I think the newbie who wrote the code simply forgot to add this check to the code, so all unfamiliar characters generate an error.
I have tried now with a bunch of different combinations, and this indeed seem to be the problem. So try removing any event in your calendar that have these characters and see if the problem goes away
you need to add your email account in iCal (= add a calendar), and activate invitations download in Preferences/Advanced, and then invitations show in iCal.