Cannot read systems for a solution (Error &1 &2)

What causes this issue?

An error occurred while calling the function module
DMD_GET_SYSTEM_INFO. The system cannot read the list of systems for a
specified solution.

System Response

Error 1: unable_to_open_model
Error 2: object_type_not_found
Error 3: no_authorization
Error 4: internal_error
Error 5: communication_failure
Error 6: system_failure
Error 7: Other

How to fix this error?

Check the solution key and the RFC destination for the solution manager
system.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.