$ adb devices
adb server is out of date. killing...
cannot bind 'tcp:5037'
ADB server didn't ACK
* failed to start daemon *
ps aux | grep adb
greg 72550 0.0 0.0 611164 1508 ?? S 4:14PM
-s 192.168.56.102:5555 shell
greg 72523 0.0 0.0 635956 2296 ?? S 4:14PM 0:00.02 adb -P 5037 fork-server server
Try running this:
killall -9 adb
That should remove all running traces of the daemon
Edit: Best solution below
This issue may be
adb incompatibility with the newest version of the platform SDK. The best solution for this issue with Genymotion is to set the Android SDK within Genymotion to your location. This can be found within the Settings page.