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Your controller firmware is 126.96.36.199 which means you are using the 5.1.0/2 that is SV 5.1 Rev B version of Control builder.
However you said that you are on SV 5.1 FP4 which means that you should get an option to load 5.1.1110.0 version of the firmware.Is it when you try to load this firmware that you get the problem.
If yes then the system extensions for AC800M connect for FP4 will not be loaded in the system.You can check this by going to the admin structure -->Domains-->system name and click on the Systen Extensions.
Please make sure that AC800M connect version 5.1.-1 build number 111000 is both installed and loaded.