Problem with 1747-SDN Devicenet Module

I have a problem with a 1747-SDN module, the module light is blinking red, the net light is red and module show a code 91. I check the indication of the lights and appears that the module may be defective(red net light). I need a second opinion before i replace the module.

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.

This manual can be very helpful if you do not already have it

http://www.ab.com/support/abdrives/files/DeviceNet_Troubleshooting.pdf

My reading would point to 2 nodes with the same address, but work your way thru the manual to confirm it for yourself

edit
I see Ken has beaten me and he is the guru here