Unplug the receiver and try a different USB port.
Uninstall SP2, SP1 , delete the simconnect folders from the winsxs folder and run a repair install to recreate these. To cut a LONG story short, the repair never installed these folders and I had to restore them from a backup. Still, no trackir.
I also tried installing the simconnect.msi from the SDK... that didn't work.
So in the end I reinstalled my Vista system. After installing FSX (and SP1) and trackir it worked... but... after installing SP2 Trackir again fails to see that FSX is loaded.

So how can I finally get TrackIR to work with FSX on my system? I need SP2 because on of my addon planes requires this.
thanks!