Select at least one organizational unit

What causes this issue?

Select at least one organizational unit.

System Response

The system responds with an error message.

How to fix this error?

Enter at least one organizational unit. If you enter multiple
organizational units, please note that they must all be located in the
same country.
A unique country entry guarantees that the document status will be
displayed correctly.
This is only possible if you maintain the following objects for the
respective country (importing country in 'Import Monitoring' or
exporting country in 'Export Monitoring'):

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

<DS:TRAN.VI29>Foreign Trade: Incompletion Procedures for Document
Data</>
<DS:TRAN.VI49>Foreign Trade Data - Control System Response</>
At this point, make sure that the indicator <LS>Save incompletion
log</> is also selected.
Not setting the indicator could lead to a discrepancy between the
status in the document itself and that in the list.
This detour around incompletion was chosen for performance reasons.

Error message extract from SAP system. Copyright SAP SE.