I had this problem too.
Solution:Press ctrl alt del and bring up the processes. Search for any instances of Crysis2.exe (I had 3 running at 100k) and click "end process" for all of them. Then try to patch again and it should work!
My guess is that it couldn't delete the original exec because it was somehow in use, when renamed it could be deleted, and the copy of it was a fresh version that also wasn't in use.
Not sure exactly what was stopping the exec from being deleted though

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Well, that kind of makes sense in a demented "Crytek" way. I used both Task Manager and Process Commander to see if Crysis2 was running, but nothing showed up.... I guess it might have been tucked away in some hidey-hole of system memory O_o.
I suppose a POR would have fixed it too... if it happens again, I'll give that a shot before I post. Thanks for the replies. I'm off to try and finish the SP before something else breaks...