QUICK TIP: Can’t Delete SharePoint Content Type – The content type is in use
Have you ever tried to delete a list in SharePoint and you know that’s the only list that is using a particular content type – so you want to remove the content type as well – maybe to start over, or just to clean up things a bit?
Even after emptying the recycle bin – I still found that SharePoint still thought the content type was being used.
I finally discovered that emptying the recycle bin doesn’t truly remove the items in it permanently. You have to click the ‘Deleted from end user Recycle Bin’ Link in the left nav and remove the items you want from there.
Give that a shot and then you should be able to remove the content type that was associated with this list.