Error Reading Scenario File

[Herr Straße Laufer]

How about doing the map fix that is located in the "important" threads area above?

Sounds like a version conflict. If it's the map then the units will be seen and you can play the scenario. If the conflict still exists it could be an OOB problem? Some custom scenarios are designed with mods and OOB changes that would make them unplayable unless you had the OOB changes downloaded into your game folder.