[Koha] Error with repeatable MARC tags

Hi everyone, I'm new to this list. I've been working on customizing Koha (2.2.9) for Windows, and have run into a problem that was posted by someone else last year--but I can't find a reply to it. Would anyone be able to help? This has to do with the MARC tags which are set to repeat in the bib framework. When I click on the + sign to repeat the tag, nothing happens and I get an "error" message at the bottom. Repeatable subfields are working fine. Thanks in advance! Jennifer