Error when communicating with Landscape Directory

What causes this issue?

An error occurred when communicating with the Landscape Directory.
Error text:
<NP>rfcdest = &v1&</>
<NP>host = &v2&</>
<NP>port = &v3&</>

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?

Check that the Landscape Directory is functioning correctly.
Check that the <DS:TRAN.SLDAPICUST>server address of the Landscape
Directory</> for HTTP requests is correctly maintained, and that the
logon data (user and password) is valid.
Use transaction <DS:TRAN.SM59>SM59</> to test the RFC connection
<NP>&v1&</> to the Landscape Directory RFC adapter.
Also check possible Landscape Directory error messages.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.