I have got a similar issue.
I'm new to City Engine and just working through the tutorials.
When I started practizing a few hours ago, everything worked fine, but now, the models won't display correctly any more. Only wire frames, no textures or shades. Additionally, there are black polygons flashing on the screen, thus making it very hard to continue working. These graphic issues are only present in City Engine, in no other application I use, so I do not think that there is sth wrong with my PC or graphics card.
I've got 8 GB of RAM, Win 7 64bit and a HD 4890 graphics card.
Restarting, reloading or just regenerating the scenes or buildings do not help.
Thank you for any suggestions!