Flag VALEXI is reset as no fixed values exist

What causes this issue?

The flag VALEXI in the system data specifies whether values exist
for a domain or not.
This flag is set, but no values exist for the domain. An
inconsistent state such as this can arise only if system data are
modified directly with a program.
To achieve a consistent state flag VALEXI is automatically reset.

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?

Error message extract from SAP system. Copyright SAP SE.