From a MikroTik AP running RouterOS 4.5 with an XR2,
feb/22 21:28:43 wireless,debug wlan1: denying assoc to 00:15:6D:DC:C9:13, does not support all basic rates
I checked that particular Ubiquiti CPE and it seems to be configured correctly.
G mode only is set on the AP and there are no associations.
A Google doesn't reveal anything useful and it doesn't seem to be documented at site:mikrotik.com.
Thanks in advance for your thoughts.
kind regards/ldv