An error occurred

Creation of MARCXML Record failed: Field 520 must have at least one subfield at /usr/share/perl5/MARC/File/XML.pm line 481. at /usr/share/perl5/MARC/Field.pm line 107. MARC::Field::new("MARC::Field", 520, " ", " ", "a") called at /usr/share/perl5/MARC/File/XML.pm line 481 MARC::File::XML::decode("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\x{a}<record\x{a} xmlns:xsi="..., "MARC-8", "MARC21") called at /usr/share/perl5/MARC/File/XML.pm line 163 MARC::Record::new_from_xml("MARC::Record", "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\x{a}<record\x{a} xmlns:xsi="..., "MARC-8", "MARC21") called at /usr/share/koha-3.22.13/lib/C4/Record.pm line 211 eval {...} called at /usr/share/koha-3.22.13/lib/C4/Record.pm line 211 C4::Record::marcxml2marc("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\x{a}<record\x{a} xmlns:xsi="..., "MARC-8", "MARC21") called at /usr/share/koha-3.22.13/lib/C4/Record.pm line 653 C4::Record::changeEncoding(MARC::Record=HASH(0x8cac830), "MARC", "MARC21", "MARC-8") called at /usr/share/koha-3.22.13/opac/cgi-bin/opac/opac-export.pl line 67