In my case the wireless connection sometimes isn't available.
To solve this, I have to extract the Apple Airport Express from mains.
And reinsert it again. In 2 minutes the wireless connection is up and running.
If I'm correct all are connected by ML.
Try disconnecting ML.
Leave it for 15 minutes, and then reinsert them.
Or disconnect both systems from mains.
No longer then 10 minutes, otherwise you have to enter your PIN code.
Hope you will figure it out.