[Koha] The following fatal error has occurred:can't call method

I'm from Benin at Songhai Center library. Currently we installed Koha 3.00.02.012 on Ubuntu 8.04 LTS. I was successful using the manuals for installation. But when the librarians are adding or editing an item in to the database, it will show us: "Koha error The following fatal error has occurred: Can't call method "append_fields" on an undefined value at /usr/local/share/perl/5.8.8/MARC/File/SAX.pm line 92. Apache Server version: Apache/2.2.8 (Ubuntu) Server built: Aug 18 2009 14:18:10 Koha 3.00.02.012 Koha DB 3.0002012 MySQL mysql Ver 14.12 Distrib 5.0.51a, for debian-linux-gnu (i486) using readline 5.2 OS Linux sahel 2.6.24-24-server #1 SMP Tue Jul 7 20:21:17 UTC 2009 i686 Perl 5.008008 '' Please any help!