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What causes this issue?

A Remote Function Call (RFC) to backend system terminated with a
communication failure exception.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

In most cases the exception text indicates directly the problem root
cause.
If not, run the so-called "Connection Test" for the currently used RFC
destination from within transaction SM59 to get more error details.
Contact SAP Support if you can't solve this issue.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.