In response to post #9662423. #9663032 is also a reply to the same post.
Well, it clearly thinks your FalloutNV.exe does not match the Steam install. Perhaps you should try invoking Steam's "Properties" / "Local Files" / "Verify Integrity of Game Cache" function if Steam is where you got it from, as suggested by the error message. The idea being that the most current (i.e. correct) .exe will then be installed.
If the game was not gotten from Steam ... then you might be out of luck. I suggest at least searching the other posts here for that error message to see if others had the problem and how things were resolved; click the orange text "View Forum Thread" link above and then perform the search.
Edited by Athelbras, 19 October 2013 - 05:24 PM.