It is possible that a company in Germany can have a plant in France, because of that and the taxes that I mentioned earlier SAP has to know in which country this business case has to be reported. And for this purpose the EKKO-LANDS field is used.
Basically it is taken from the plant T001W-LAND1 when the PO is created.
SAP has to make sure that such a PO does not have items with plants from different countries.
So SAP takes the plant of the item and retrieves the LAND1 information from T001W table. Then it compares this value with the value stored in EKKO-LANDS, and if this differs then the error message ME552 is issued.
SAP has a correction program in OSS note 199642 - ME22: ME552 / EI196 (inconsistencies in EKKO-LANDS)