I think I know the problem!

You probably built with "Lit Maps only". Thats why your problem only happened in your WMB but not when someone else built it. Your map is very dark and was below the shadow threshold. It just didnt look as dark in your shot because it was lit by the dynamic light and the ambient.

But when you added that static light, the place under that car was just bright enough to get a shadow.

The solution should be simple, either set your shadow threshold at 0, or dont build with "Lit Maps only".

Hope this helps.

That's it ... thanks for helping.

Regards,
Pegamode.

Only just on-topic, but I always leave "Lit Maps only" unticked.
In what situations would you ever turn it on? (Im only noob at level building)