Looks like you may have a video driver problem. I only use Mint and SuSE, so I can't really say.
Finally, after 4 days struggling. This morning I authorised updates on unbuntu and installed them. And Flash and Adobe Air and works again fine...
Today In rebooted again the server, and the problem showed up again...
I finally find what the problem was. It has nothing to do with either the server, neither Flash Player or Adobe Air.
The problem came from mstc window (remote desktop software). By default it was set to display 16bit colors. I might have changed it sometime to 15bit.
By setting it to 16bit, it solved the problem.