[Koha] Hello / marc import problem

Hi there, I am helping a school setting up Koha for their 6000 books library. We are nearing the stage of production with installation, labels, importation, daily management etc under control, thanks to Koha. So KUDOS :) The last thing we need is to import records from Bookwhere (a Z ). I can stage a batch of records, the records appear in the managing batch as expected but no matter what, clicking on "import into catalogue" will give me a 0 number of records added, updated, ignored and the same for items. Obviously, I don't find my records in the catalogue. I don't get any error message in koha_error-log, so I wonder if I am missing something obvious? btw, my koha version is 3.00.04. Thanks for any help. Take care, Joel