Unexpected error 13:6 — how do I fix this?

Ah the good old-timer Tages is giving you a hard time. Not a problem, there is a solution.
Error 13:6 is a common issue with products using Tages copy protection system. To fix this please visit this page and download the latest version of Tages drivers.
Make sure to choose the version which is suitable for your operating system (32 or 64bit). Install that driver and repeat the game's installation.