[Koha] Unable to input MARC field

[Stew Wilson]

Hi Everyone,
I'm very much a Koha newbie, so sorry if it's a silly question:

I have made myself a customised MARC framework.  During this process I
accidentally deleted tag 260.  So I added it again as a new tag and just
copied the details from the default framework.  So now when I go into the
edit record screen of a book I can see tag 260, but I can't add any
information to it.  I can see a cursor in each subfield, but I can't type
anything into it.

I guess this is something to do with authorities, but sadly I have no idea
if this is true, or how to fix it.

Is anyone able to point me in the right direction?

Cheers,
Stew