Nuendo, Sync Station and AjA KiPro Rack


I have a strange problem with Nuendo on a MacPro, Syncstation and an Aja KiPro Rack Video Recorder/Player.

I want to start the recording in Nuendo and at the same time the video recorder starts to record.
And when I’m finished recording I want to play back the material from Nuendo in sync with the video
(Viritual Sound Check with Video)

The problem is that nuendo in “sync mode” don’t record as it should.
Sometimes it records 1 ch for an hour and then jumps out of recording or 1ch for 2 seconds and then out.
Or I have tried to record 40 ch and the same problem continues.
The video recorder records fine!

But the strange thing is that it records fine alone (no external sync)

And even if I disconnect everything from the sync station the problem is still there!

The setup

Mac Pro with Nuendo and RME HDSPe FX MADI 96kHz
Syncstation connected with USB to the computer and RS422 to the AjA video recorder
Sync Station LTC in from Alperman Velte video master clock
Sync Station LTC out to AjA Video Recorder
Video sync from Alperman Velte video master clock

Grateful for your help