Help RS-485 Network Troubles?

Hello everyone, I am new to posting so I hope I get y'all the info you need. I have some Escort HMS-820 RFID Reader/Writers on a MM80 MicroMux Network communicating to a GE Series Six ASCII Basic Card. I have one Node on my network that is constantly failing Readers and Communications. I have talked to BB Electronics and according to their recomendations I am installing OptoIsolators on each node to help increase my line bias. Anyone else have any ideas? I am getting hammered for these failures and it stops part of the plant. Thanks 9600 Baud 8,1, and None

my first questions would be is the devices daisy changed or in a star configuration. the devices should be daisy chained. next would be terminating resistors. you should have a 120 ohm terminating resister on each end of the circuit. some equipment has the resistor built in so you may need to check and see if it is enabled or not. is this 4 wire or 2 wire?

More Info

Using 2 wire with Signal Ground,Daisy Chained, 120 ohm resistor was installed on one end of cable. 900 foot total cable run. Seperate conduit for Belden 9184 cable. Each breakout box uses Belden 8103 cable to power and connect each of the readers. Fiels connection is using a 9 pin dsub connectors. Checked my Line Bias and it was very low aroun 70 millivolts. Leading edge of each Square wave signal has a sharp spike but then rest of Square wave looks perfect. I hope to be able to post pics from Fluke 123 scopemeter just have to learn how. thanks

Some good info in PDF below. Trouble shooting guide from BB.
Pay special attention to the termination and biasing parts.

In FlukeView software, right-click on the waveform display you want and select 'Copy Graphics'. Then use Ctrl-V to paste into MS-Paint or your favorite graphic editor and save as a GIF or PNG file for posting to the Forum.

If this is a multidrop system it's going to be difficult to get the scope to capture the signals from the device that is "dropping off" the network instead of the ones that are working fine, unless you can reduce the system to that one device.