I used the Opus admin option to elevate for a few minutes, opened a folder from Program Files (x86) on my Win 7 64bit system, and then renamed a file, using the same name as an existing file. When the rename dialog appeared, I clicked Replace (Delete Existing File). I then receive an error - 'an error occurred deleting readme.txt, an unknown error occurred' (readme.txt was the file I was trying to overwrite). I can then only skip or abort (retry does nothing). Oddly, the file was deleted - but the file I was renaming was not renamed, so the process does fail.
An associated problem is if I created the copy of the file by copying and pasting the original file - after I receive the renaming error, if I then try to paste the file again (to re-create the deleted readme.txt file), I get the same error, except this time the text is 'an error occurred copying readme.txt, an unknown error occurred'.