[Koha] newbie: items from Follet export

[Nigel Barker]

Dear List,

I've been trying my best to crack this.
I have a library that works. I can use the ISBN to lookup and import a
new book, find it in opac, check it out, etc.
I used Marc Edit & co. to modify some Follet data, specifically to
ensure that the mandatory Koha 952 fields are there. I used the
existing Follet barcode from the 852 field. Then I staged and imported
those records and items, using a book with several copies (ie.
multiple 952 lines).
Now opac shows items available, but no physical holdings (which is
confusing me - what is a physical holding - not an item?)

In cataloguing/circulation, however, the barcodes don't work  (barcode
not found). When I search by title and select the record, I can see
item details, including the barcodes. From here I can delete an item,
but when I do that, the other copies are also deleted! If I try to
edit an item, I get this error:

"Can't call method "subfield" on an undefined value at
/usr/share/koha/intranet/cgi-bin/cataloguing/additem.pl line 607."

I can edit the books I added by hand, just not the ones from the Follet import.

Is this enough description for someone to recognise where I am going wrong?

I feel like I could have scanned all 11,000 books in by hand in the
days its taken me to fail to import this data!

Thanks

nigel