[Koha] Tag " " is not valid in koha/lib/C4/biblio.pm

Hello, I have a little problem when I want to save my biblio record (from my own MARC framework) . An error appears: Tag " " is not a valid tag at usr/share/koha/lib/C4/biblio.pm line 1864. This line (in this file) is the next: & GetMarcFromKohaField ("biblio.biblionumber", ' '); What's the error?? What can I do even if I'm not the webmaster but the librarian? Thanks Martin Caris