Error while trying to delete a Doctype element

Hi! I’ve found myself with a problem that I cannot understand how to resolve. I’ve made a doctype and I was testing it by creating elements everytime something was changed. At the end, the doctype does what I need but I cannot delete the elements created under the older versions of that doctype. At least, that’s what I think the problem is. How can I resolve this? I have no idea how to access a file explorer o something similar because we don’t work in the core of the framework (I don’t know if I’m talking about what I want to express, sorry for that).
This is ‘doctype not found’, when I try to delete the element:

These are the elements:

And this is the error when trying to access one of them:

  • ‘doctype not found’, ‘the resource you’re looking for it’s not available’

Please, let me know if I’m not being clear enough. Thanks!