Sketch-Upload over WIFI not working

Hello all together,

I recently bought a Yun to control the lights in my room via WIFI. For this purpose, I want to upload new sketches to the Yun via WIFI too. The first time I tried this with the Arduino IDE it worked, but not anymore. The "Board" is set to Yun and I selected the WIFI connection at the "Port" menu. But everytime I want to upload the sketch I get the error:

avrdude: AVR device not responding avrdude: initialization failed, rc=-1 Double check connections and try again, or use -F to override this check.

Uploading the same sketch over USB is working fine. Even the Bridge example is working with the WIFI connection, but uploading a new sketch fails.

I am trying to upload via Arduino IDE 1.5.6-r2 on a Mac (OS 10.9.2).

What can I do to get this working?

Thank you in advance.