Incorrect code page &1; must be a system code page

What causes this issue?

A system code page is necessary here.
A code page is a system code page if one of the following conditions is
met:
the code page is in the column CHARCO of the table TCP0C; this table
contains permitted configurations of platform, language, code page,
locale, and so on.
the code page is on the list of known code pages, table TCP00, and has
the attribute CPISSYSTEM.
Note 1047012 contains further information.

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

System Response

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.