Hello Nayef Yahya;

Is this the same issue you had 3 months ago, same project, same DP/DP coupler?

https://support.industry.siemens.com/forum/ca/en/posts/db-db-coupler/277728/?page=0&pageSize=10

"I solved it by download OB82 and OB86 to both CPUs".

What has changed between then and now? Did the addition of the diagnostic OBs not fix the problem permanently?

Without the diagnostic buffer information, all you can consider are the diagnostic LEDs on your unit, and you should look at what they mean, singly and in combination, in the  dedicated manual; look at the screenshot below.

- DP/DP coupler manual

https://support.industry.siemens.com/cs/ca/en/view/1179382

The solution proposed most likely reuires yu to look at the diagnostic biffer on both your CPUs, to fins out what your system is complaining about. 

To help you out correctly, we need to see more information.  Please prepare a pdf or Word file containg a sketch of how the DP/DP coupler is used between 2 seperate CPUs (as Profibus-DP masters), a screenshot of both hardware configurations showing the link between a CPU and one connection of the DP/DP Coupler, and the sections of both diagnostoc buffers that relate to the iDP/DP coupler messages.

Hope this helps,

Daniel Chartier