I haven't seen this exact problem (I have Shredder 12 UCI for Windoze), but it almost sounds like the program makes book moves, and as soon as the engine needs to make a move, the engine doesn't do anything. Have you activated the program with your name and activation code?
P.S. Stefan has always been responsive to me in the past. Did you give him a day or two to respond? (He might be busy with something at the moment.)
I just bought Shredder Classic 4 for mac and it only will play the first four or five moves, it will sit there until time runs out. I'm new to Shredder and it may be a setting thats wrong. But it is very strange that after it makes its last move the notation goes red. I have emailed support many times with no response from them, has anyone seen this or know about this problem??