When you download Minecraft for Mac, you download an application file which you then place in your Applications folder. But that's just a wrapper for the "real" Minecraft binary files (a set of JAR files), which gets downloaded into your Application Support folder.
So when you delete and redownload the Minecraft application, you haven't done anything about the actual binaries already downloaded and being used. If these are corrupted (as they appear to be in your situation), they won't be fixed by redownloading the Minecraft application.
While "Force update" should do something about these files, you can do something about it yourself by manually deleting the downloaded JAR files.
To do this, you'll need to navigate to the path described in the error. In Finder, go to the Go menu and select Go to Folder... Type in the following:
~/Library/Application Support/minecraft
and click the Go button. Finder will open a new folder with a few subfolders, including one labeled bin. Throw the bin folder in the Trash and empty it.
Now go back into your Applications folder and open Minecraft. Minecraft will then redownload its binaries and the problem should be resolved.
To re-download your .minecraft folder you have to do a force update. You can find that by clicking "options" in the launcher. Without a forced update, the launcher might only check to make sure you have the latest minecraft.jar and will only download that if it's out of date or missing entirely.
If you deleted it when minecraft is open, Delete the folder again and force update.
Best Answer
To restore Minecraft files just run the game from the launcher. It will download any missing files.