For a long time, Zurich V1 and Geneva were both running without any issue. For other reasons, I decided to scratch and reinstall FSX ( Windows 7, 64 bits).
Zurich V2 was installed, with Addon Manager 2.8.06: wonderfull.
Afterwards, Geneva (latest download) was installed: fine again.
Finally, I moved back to Zurich...Ground Zero

! No building any more.
Back to Geneva: all right.
I don't understand: were is my error ? Can you help me: many thanks.