Is this a new installation, or has this system been working ?
Status code 91 is a "Bus Off" error indicating the 1747-SDN cannot transmit or receive data on the network. Carefully check the continuity of the blue and white wires in the system. With the power off, check the resistance between blue and white at the scanner; it should be about 60 ohms.
With the Module LED blinking and the Network LED solid red, I think there's about a 50% chance the module has been damaged.
Check the network as advised above, but be ready to replace the module.