In some very rare cases the installation of the game cannot be done due to very specific system configurations regarding the copy protection. As the DVD has been manufactured also in English and French, this problem might also occur with the retail version sold in other parts of Europe.
The occuring error is that Windows requests to insert the original game into the hard drive - even if the DVD is already inserted. This error may also occur in very rare situations after you have already played the game several times before without any problems.
If you have renamed the installation directory during the setup process of the main game, please rename also during the installation process of the patch. Ususally, the default is set: /Programs/Kalypso/Imperium Romanum.