Period & is not allowed

What causes this issue?

The period entered (&v1&) is different from the period calculated (&v2&)
and is also not in the interval for special periods (&v3& to &v4&).

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

System Response

Error.

How to fix this error?

Correct the value entered for the posting period.

Error message extract from SAP system. Copyright SAP SE.