1] delete the .cityengine folder in the user account 2] create a new workspace, move and relink the projects.
My name is Leilei and the navigator in my CityEngine has the same problem. I've been using it for a year now and this navigator error appeared earlier today. I tried the method you said above, but it still has the same error. Could you give me some instructions on how to solve the problem? (my CE is 2013 version)