Hello,
I have issue with registration in Wireless interface since I have upgrade from 6.27 to 6.28. 
So I decided to downgrade to 6.27. Unfortunately I noticed that Winbox couldn’t find my RouterBoard and the power LED flashing.
I have done Hard reset on device and I have always nothing in the LOG window about wireless interface.
I attached a picture with my config and LOG window showing “start CRL update” but nothing on my wireless interface. 
2015-04-26_16-17-47.png