We had this problem a few releases back with the Force 300 connecting to the ePMP 3000 AP’s. SM’s did not want to connect if under a -70dbm RSSI. We got the same error message.
what is SNR? It is quite tough to answer such question with out additional info.
You can try to post here Monitor Wireless and Performance pages from AP and SM.
Also is there anything else in syslog on both sites. How is the spectrum there?
The SNR 27 RSSi -67
Sys log form SM
Sm cannot be associated on AP F=5510 11acvht Reason : 16 ( INA Retries exhausted)
Sys log from AP
aid =1 dusassociatef Reason :52 (INAC miss timeout)
You have to improve your signal! Try to check if you are not on a side lob and for interference.