Why is the Plugin Installer Corrupt or Incomplete?
Most likely the download didn’t complete – you only have part of the plugin. The first thing to try is download it again here. After it finishes downloading, open and run it then follow the instructions. Sometimes the browser gets confused and won’t re-download the plugin. The result is every time you try to download the plugin, it appears to download instantly but it is still corrupt. To reset your browser, you need to clear your browser’s “cache” or “browsing history”.