SAP Note 11006 - Posting to special periods not possible using MR01.

Symptom

When the user attempts to post an invoice using MR01 to a period defined
as a special posting period, the error message M8 022 appears: Allowed
posting periods..
The invoice cannot be posted to a special posting period.

Cause and prerequisites

It is not possible to post an invoice to a special posting period using
MR01.

Solution
An invoice must be posted in all cases to a period defined as a
normal posting period (and not as a special posting period).

Key word: Special periods