Thank you all for your feedback. I have since updated the
xorg-x11-drv-intel and libdrm from the elrepo, which has solved the
problem. flash player 11 now runs successfully. The cpu usage is a bit
high e.g. when acessing the right click menu in full screen mode it is a
bit laggy, but otherwise it is good.

jon

On Thu, 2011-07-21 at 17:21 +0200, Dag Wieers wrote:
> On Thu, 21 Jul 2011, jonathan wrote:
> 
> > Upon upgrading from flash-plugin-10.3.162.29-0.1.el6.rf (x86_64) to
> > flash-plugin-11.0.1.60.0.1.el6.rf (x86_64), when i switch to full screen
> > mode when playing a video on for example youtube Xorg freezes.
> >
> > When using flash plugin 10 the use of "OverrideGPUValidation=true" in
> > the /etc/adobe/mms.cfg file fixed the problem. Though it does not fix
> > the problem on flash-plugin 11.
> >
> >
> > If the compiz window manager is used fullscreen playback works.
> >
> > Any suggestions?
> 
> Sorry Jon,
> 
> Let me clarify that this Flash update was very much needed, even though we 
> go to another Beta. The problem is that the 64bit plugin (square alpha) 
> had lots of security issues. Undoubtedly this release will have some too, 
> but at least anything known is fixed in a more recent release.
> 
> Here's hoping Adobe will take care of 64bit platforms soon with proper 
> security updates...
>