What are you trying to do with them ?? (from the error message it would seem you are trying to open\play them and that is why you get the error - they are saved in a format that only he game understands so you would need to load them in the game to use them.)
But you do not need a CODEC to copy or move the save game files - just right click on one of the .ess files and select copy and then paste it into the new folder where you are trying to place them.