Hi Eckbert,
Q: Only if the parent already exists in the BU structure the records are imported. So you have to repeat the import activity several times until the whole tree is imported as records that are the parents of following records in the csv file hav not yet a parent in the existing crm. That's very angry.
A: If you're importing data all the records will be first validated if the lookup value (in your example parent organization) which you would like to point exist. It means you're allow to import only per single level of BU tree view.
If you have a very complicated BU structure you can consider custom application which you will create all the BUs and relationships between them.
OR
use import all your BUs as top level BU (with no Parent BU) and use this tool to update Parent BU
http://mscrmbulkupdatetool.codeplex.com/ Q: Importing existing BU records they get not updated as there is an error in the protocoll.
A: Bulk import in MSCRM not have possibility to update the records only to create new but you cannot have 2 BU with the same name. Here I can suggest codeplex free import tool which can update records !!!
http://mscrmbulkupdatetool.codeplex.com/
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