This isn’t an error. It’s just a notification that the project was made in a lower version of After Effects than you have. That allows users with older versions to use these projects. Since you have a new version than CS3 , After Effects is upgrading the project to your version. You will have to save your project as a new file.

The file is compatible with Mac and Windows platforms, but previously had issues unzipping on certain Windows platforms. The file has been fixed, so if you’re still having trouble, re-download and try again.