This looks like the APIs used to 'check status' on rented movies is what is causing the issue (at least on mine) since the error reports all point to a Quicktime issue in checking movies and movie states. I haven't used the rental feature, but I did migrate all my computer based movies to iTunes a while back to be able to catalogue them and use one interface to view them.
This is further supported by the 'announcement/fix' posted
here.
So, you can either remove all your .mpg and/or .mpeg files (hopefully not .mpga files) or revert to iTunes 7.5.x.
I wonder when iTunes 7.6.x is going to be released to resolve this "little" glitch.
peace