Panel to Panel networking and communication

[ashudwd16]

Dear all,
i have 4 EST3 panel and i want establish networking- communication among all panel.
3 Panels are communicating to each other on fiber optic cable but 4th one is not communicating.
4th Panel is properly working on its location and 700m apart from an other panel.
i Have checked and done following exercise:
1. All optical fiber cable are healthy.
2. 3 FIBMB2 and MMXVR module are healthy.
3. Optical fiber interface card with flat ribbon cable are healthy.
4. Light intrface unit to MMXVR module patchcord is also healthy.

Then where is the issue,why panel is not communicating to another panel.