FATAL ERROR: Could not load world file 'maps/main/config'

[jens]

There is no such file so it indicates that something has been edited or perhaps a total conversion been installed or something that makes it want a file that is not part of the original install.

Try to uninstall the game and then go to the Steam folder commonapps and check so that there is no Amnesia folder left, if there is then manually remove the whole folder. After that remove any settings files you have in documents/amnesia/ and then install the game again to make sure you have a clean install.