Good news for Windows users!
The latest version (11.5.6) of the Shockwave plugin for Windows fixes the issues that were causing problems in earlier 11.5 versions.
The game will take you to the download page if you need to install it.
Mac users are still out of luck, as the 11.5.6 version for Mac was not fixed by Adobe. The 11.0.3 version, however, still works. For more info see [www.conquerorgame.com
Also note that Firefox causes problems on the Mac. Safari is the recommended browser for Mac users.