Any Idea why this error is coming while registering instruments
From the error, the application was unable to send a request message due to the channel or connection problem. The connection may be down. You need to verify if the application received the channel down.
Normally Developer Community Forum is for how-to/general questions but your question seems to be more complex and requires investigation e.g. review source code, configuration, try to reproduce the problem etc.
I recommend you contact RDC subscribers in your company to raise a query through the premium support service. RDC subscribers should see a link "Contact Premium Support" when they are logged into the developer portal (https://developers.refinitiv.com/elektron/elektron-sdk-java).
For any difficulties submitting the query to us, please contact email@example.com.