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.
Best Answer
Pre 1.6 (Old Launcher)
If you deleted your
bin
directory it will be recreated when you launch the Minecraft client.If the client starts up, your
bin
directory is almost certainly at:C:\Users\You\AppData\Roaming\.minecraft
or%AppData%\.minecraft
~/.minecraft
~/Library/Application Support/minecraft
Post 1.6.1 (New Launcher)
The new launcher does not create a
bin
directory. Instead, there is one folder for every installed different version of the game, located in the folderversions
in your Minecraft directory (see above). For example1.7.10
, or14w30c
. Note that multiple profiles can use the same version and there will only be one folder.