I'm not sure what I've clicked (something like a paste function perhaps?) but I can't delete a textbox. I've tried clicking delete, and unlocking everything on the page - but none of these options work.
When I drag the textbox, a duplicate is created. These duplicates can be deleted when I click delete on my keyboard, but the original one simply cannot be deleted.
Any ideas of what I've done/how to fix it?
I'm not sure what version of InDesign you're on but it's always a good bet to use File>Export (Cs5.5 and earlier) or File>Save As (Indesign Cs6 and up) and choose InDesign Markup Language (.idml) and then open that and see if it fixes the issue.
Might be worth looking at the Layers Panel for any locked objects - http://www.wikihow.com/Unlock-Objects-in-InDesign
The other thing is to look on Master Pages for it.
Thank you, Eugene. None of these options quite worked, but when I randomly clicked on "move to the back" I was able to delete it. Thanks for your help nonetheless!