The error message is probably wrong.
There are no invalid runway surface defined in Geneva. There's an "unusual" runway surface used for one of the runways, which is grass, which is correct, since there is a grass runway, and it's a 100% legal runway surface to use, as defined in the SDK, and it it were wrong, the BGL compiler would have flagged it.
You can disable the error report, by unchecking the "Content Error Logging" in the General area of the Settings. I think this feature was in fact supposed to be off by default, it might have slipped away in the final release by mistake, since it's more useful to developers to test their products (and in this case, the scenery is 100% correct), and it might potentially have some effect on performances.