Enter acquisition year

What causes this issue?

In the definition of the level of the calculation key, you made at
least one entry that has no specification for the validity period of
the acquisition (acquisition year).

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?

Enter the required year.
Please note that this is a 'To' entry.

Error message extract from SAP system. Copyright SAP SE.