Have a look if the text is not locked on master page or on a spread.
Go to Object>Unlock All on Spread.
See if that helps.
Unfortunately that isn't possible. It doesn't seem to be a possibility to unlock any objects. As a matter of a fact, it isn't even possible to mark the text. I really don't know what to do.
But thank you for trying
Have a look if you can find it on any layer and try to switch it off in layers panel.
THANK YOU! This solved my exact problem too.
I'm having a similar problem in InDesign with the Square Catalogue Layout. I am unable unlock the headers so I can change them. Can you help?
If I search for 'Square Catalog Layout', Stock returns quite a number of possibilities. Could you link to the one you are trying to use, so I can have a look.
Chances are the headers you are trying to edit are in one of the master pages, so I would recommend that you check which master(s) is applied to your catalog's pages and open the master directly to try and edit the headers.