Macbook Air (Mid 2011) and DisplayPort External Monitor Problem

Hi Folks,

I've got a Macbook Air (Mid 2011, OS X 10.7.1, with all updates) connected to a Dell E1909WDD Monitor. The monitor does not display a thing and OS X does not register any connected monitor. This monitor is DisplayPort *ONLY*. I've got a mini-Displayport to Displayport adapter that works just fine with a previous generation MacBook -- if the older computer is connected to the monitor, Lion picks the monitor up, and it works perfectly. But nothing on the latest generation MacBook Air.

Also, if I connect the thunderbolt display to another monitor (say, through a mini-Displayport to DVI connection), everything works fine. So the Dell E1909WDD works independently of the Macbook Air, The Macbook Air works independently of the Dell E1909WDD through another monitor, but they don't work together. The cables have all been tested through working connection.

I've reset the SMC, but nothing.

Any ideas? Any ideas why this fails?

Thanks,