Connect with 2 jtags to 2 Processors

I'm trying to connect with 2 jtags to 2 processors , BF547 and BF512, at the same time with no succes.

I have no Problem to connect to each one of them separatly.

I know that it's Posible to connect to 2 processors at the same time .

Do you have any idea what can be the reason that I can't connect now ?