Santanu:
The problem seems to be of 75176 AP And BP, when i replaced the AP with the BP in entire systems the system started working fine.
With a general interest in 485 flavors, I had a look at the datasheets for the 2 chips and I am as certain as can be that Andy is right
You need to investigate this thoroughly before declaring that you have fixed the problem.
Your underlying problem may still be present - you could just have masked the symptoms for a while...

One question: have you used the 3 resistor termination, this would be a typical issue that could be masked by minuscule differences in the 176s.

Erik

"Successful testing does not prove the abscence of bugs, it proves the abscence of known bugs.