Maint. of manual insurance value not possible in this maint. year

What causes this issue?

The maintenance indicator for manual insurance values requires entry of
the manual maintenance year.
If you only set the manual maintenance year, the base insurable value
will be determined from the manual insurance value entered for current
market value insurance. The base value is then updated by the system at
fiscal year closing.
You can generate a manual insurance value by setting the manual
insurance value indicator. This manual insurance value remains System
unchanged by the system.

System Response

You have to enter the manual maintenance year.

How to fix this error?

Correct

Error message extract from SAP system. Copyright SAP SE.