Today I had to reinstall Bootcamp, and thus create a new Windows partition.
Trying the Bootcamp setup wizard, I got the same error as I had before – “Your disk cannot be partitioned because some files cannot be moved”.
I tried to Zero-Out-Data, overwriting all deleted data on the disk with 0’s. Yet this did not seem to solve the problem.
After deleting some big files, like my heroes & 24 episodes, I tried again. Still nothing.
I then remembered I had WoW Wrath of the Lich King installed (7ish Gb). Deleting the WoW folder and trying again, did solve the problem. I didn’t even have to zero-out-data again.
So, basicly, deleting big files (folders?!) seems to solve the problem too.