If you have followed the procedure to get the latest version, did you tried to unzip the file on your PC and does the Zip is corrupted ?
If you can unzip it with sucees, the problem is not the package itself but something else that you didn't described.
Perhaps this is a problem on your PHP environment that is not able to unzip the
package that you upload.
In this case, try installing the package from a directory.
We have recently added a video in the tutorial that show how to install from a directory.
tutorial.jms2win.com/joomla/multisite-12...stall-from-directory