Audio Alchemy DDE v.3.0

I need help.
I own a Audio Alchemy DTI v.2.0 and a DDE v.3.0.

My problem is that the DDE won't get the status 'lock' if I feed my digital signal through the DTI which connected to the DDE although I still get analog output signal.
BUT if I feed the digital signal directly through the DDE (bypass the DTI), I get the 'lock' status o.k.
What wrong with my DDE? How to fix it?
Thank you.