Yep, your answer is in the screenshot 🙂 :).
Look at attachments, it says 1. No idea where it is attached to but you cannot remove a package if it is still attached to a machine.
make sure to unattach it (if you assigned it, make sure the user that had the attachments logs out) and then you will see that you can remove it.
If it still sees it as attached it could be that the database is not yet cleaned and thus still thinks it is attached.
What happens if you go to the attachment tab? Or could it be that it is still attached to a package machine maybe?