AUGraphConnectNodeInput returns OSStatus -10861

Question

I have a Audio Unit graph which looks like that:

mixer0 -> lowpass -> mixer1 -> output

The connection is done using commands like this:

error = AUGraphConnectNodeInput(audioUnitGraph,
                                lowpass,0,
                                mixer1,0);

Everything is working so far. But once a rendering callback is set to the mixer1 node using AUGraphSetNodeInputCallback AUGraphConnectNodeInput returns OSStatus -10861.

What is wrong?