Yes, but I can only narrow it down to two possibilities - - 1) Data errors due to cable defect or equalization differences when the NAD and Optima are connected. We know that the cable is outside the normal length of a High Speed cable, which makes me think bit errors are possible or 2) firmware in either the Optima or NAD have firmware issues and can't understand each other.
Unfortunately the nature of interface issues is that if you take away one or the other side of the interface and substitute it with something else the interface problem can be solved. It doesn't mean that the one thing that was taken away was the problem - just that the two that worked were compatible. That makes these types of issues difficult to troubleshoot and just takes time to figure out what is going on.
The other thing you can try (which should definitely rule out the cable) is to move you receiver temporarily closer to the projector and use a short (no more than 2m/6') High Speed cable. The shorter cable the better. If that doesn't work with the short cable, then you've ruled-out the long cable and it's probably a firmware issue. If the short cable works, then it's probably your long cable causing the issue. Cable issues are much easier to fix.