Fusion 8 PC - No comp thumbnail

Hello,
when opening (or saving as) a comp file I can't see any thumbnail neither in the main window nor in its "preview" zone.
Is there some parameter to be set in order to force Fusion to create thumbnails when saving its comp?
Thanks.
Fabrice
when opening (or saving as) a comp file I can't see any thumbnail neither in the main window nor in its "preview" zone.
Is there some parameter to be set in order to force Fusion to create thumbnails when saving its comp?
Thanks.
Fabrice