[toki]

well, it's frustrating.

First I reinstalled only Pro Tools SE, but that didn't help.

Then I deinstalled Pro Tools SE, Fast Track C400 driver and Interlock driver (from PACE), which was installed together with Pro Tools SE. And then I ran through the same steps on my normal PC an on a Windows XP PC with exactly the same reaction on both machines:
First I installed the device driver for my Fast Track C400. Then I installed Pro Tools SE. After the necessary reboot I opened Pro Tools SE and it worked.
Then I closed the program and opened it again, and it worked.
Then I rebooted the PC and from now on I couldn't start Pro Tools SE. Every time I tried ist, I received the error message.

There was no difference wether the interface was connected to the PC during boot or was connected after the PC was started.

I tried different USB ports, same reaction.

But I realized, that windows installed an update for the drivers every time I connected the device to a different USB port. That worked for the first time after successfull installation and the program still worked. But after rebooting the program never started successfully, no matter what USB port I used or if the driver was installed by windows or not.

I have no idea what to do next. I guess I have to send back the hardware and try it with a different one. Or has anybody an idea, what I could try instead?