The unit is configured as a Client and this is working fine when tested with several brands of routers and access points

However, in the production setup neither of our two TL-WA801NDs will connect to the production router,

The system log is not very helpful in displaying the cause of this.

Why is a clear reason for the problem not printed in the syslog ?

Error messages like MSG WARNU#647273 are useless when they cannot be looked up.

Why do these units not connect to our production router ?

####################################################################
#                    TL-WA801ND  System Log 
# Time = 2016-01-01  0:02:58 180s
# H-Ver = WA801ND v4 00000000 : S-Ver = 3.16.9 Build 160913 Rel.42766n 
# L = 192.168.0.254 : M = 255.255.255.0
# W1 = DHCP : W = 0.0.0.0 : M = 0.0.0.0 : G = 0.0.0.0
####################################################################

1st day 00:00:03     OTHER         INFO       System started
1st day 00:00:09     SECURITY      INFO       PPTP Passthrough enabled
1st day 00:00:09     SECURITY      INFO       L2TP Passthrough enabled
1st day 00:00:09     SECURITY      INFO       IPSEC Passthrough enabled
1st day 00:00:09     SECURITY      INFO       FTP ALG enabled
1st day 00:00:09     SECURITY      INFO       TFTP ALG enabled
1st day 00:00:09     SECURITY      INFO       H323 ALG enabled
1st day 00:00:09     SECURITY      INFO       RTSP ALG enabled
1st day 00:00:09     SECURITY      INFO       SIP ALG enabled
1st day 00:00:15     OTHER         WARNING    LAN IP and mask changed to c0a800fe ffffff00
1st day 00:00:16     DHCP          NOTICE     DHCP server started
1st day 00:00:17     OTHER         INFO       MSG WARNU#647270|
1st day 00:00:17     OTHER         INFO       Create Syslog Refresh Thread Success
1st day 00:00:17     OTHER         INFO       System Initialize Finished.
1st day 00:00:22     OTHER         INFO       MSG WARNU#647273|
1st day 00:00:28     OTHER         INFO       MSG WARNU#647365|
1st day 00:00:33     OTHER         INFO       MSG WARNU#647367|
1st day 00:00:34     DHCP          NOTICE     DHCP server started
1st day 00:00:38     OTHER         INFO       MSG WARNU#647365|
1st day 00:00:43     OTHER         INFO       MSG WARNU#647267|