Cannot read global key (see long text)

What causes this issue?

The system cannot access the global key, for which the storage location
is specified in the profile parameter <NP>rsec/securestorage/keyfile</>:
(&V1&): The file does not exist or cannot be accessed from this
application server
(&V2&): The file contains characters that are not in the permitted range
(only 0-9 and A-F are permitted).
(&V3&): The file is too short (it must contain 48 characters).

System Response

The secure storage cannot be used.

How to fix this error?

Check the file containing the global key.
Note: If the profile parameter contains an empty value, the system uses
a standard key. Although you cannot use this to read entries created
with another global key, it is possible to create new entries and to
overwrite existing entries.
If the standard key is the new global key that you want to use, you can
migrate the existing entries in transaction <DS:TRAN.SECSTORE>SECSTORE
</>.

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.