Hi @Jim_Riedmann,
In Short: The workspace is a specific folder on your filesystem where CityEngine stores projects and settings. CityEngine keeps track of all files/folder in that workspace while running. It would cause issues when another instance of CityEngine would use the same workspace at the same time, that's why there is a locking mechanism.
But this message should not appear after a fresh install. I can only imagine that the default workspace (which CityEngine creates at startup when there is no existing one) is somehow corrupted.
I suggest you to delete the default workspace and then try to start CityEngine again. The default workspace is usually located under:
C:\Users\<username>\Documents\CityEngine\
If that does not help the next step would be to also delete the CityEngine Profile which is stored under:
C:\Users\<username>\.CityEngine
Let me know if this works.
Best,
Jonas