It is an update note that comes from Corey J. Mahler, the guy who wrote the AirPort Utility 5.6.1 Launcher.
Here's the note
"It would appear that Apple has changed something in the network stack in a recent update to Yosemite. This update has resulted in AirPort Utility v5.6.1 not being able to find some AirPort Units some of the time. While this is annoying, there is a simple fix: Connect the AirPort Unit you wish to view in AirPort Utility v5.6.1 to the Mac running the utility via a wired (i.e., Ethernet) connection. I have yet to hear of any case where this has not solved the connectivity issue."
This is the link, the note is taken from
AirPort Utility v5.6.1