Are you as annoyed by this “The content type is in use” error as I am?
Error messages like this that don’t give you a way to solve the problem are a sign of the devil to me. That Correlation ID does us no good (try to find the administrator in a large organization to help you out in a timely way) and there’s no good way to find out where the Content Type is in use.
In many cases the Content Type may be in use with real content. However, in the instance where you are prototyping something and delete the list where you were using the Content Type, you know that it’s not in use anymore, right?
Well, it’s still in use, actually, but only sort of. When you delete the list, it goes into the Site Recycle Bin, so it actually still exists. It’s a great safety feature, but in this case, it’s getting in our way.
You need to delete that list from the Site Recycle Bin as well as the Site Collection Recycle Bin. The former is easy: you deleted the list so you have permission to delete it from the Site Recycle Bin.
The latter is only available to you if you are a Site Collection Admniistrator, so you may need to find someone who has that permission to help you out.
Once you’ve deleted the list from both Recycle Bins, you’ll be able to delete that pesky Content Type. Of course, you can also wait the requisite 60 days until the list is deleted from the Site Collection Recycle Bin automatically (by default – your settings may vary), but who will remember that far into the future? And we all know that a clean Site Collection is a good Site Collection.