Whenever you create a Workflow that “Assigns a To-Do Item” in SharePoint Designer, SharePoint behind the scenes will end up creating a Custom Content Type for you.
However, one of the problems with this is that if you end up renaming the “To-Do Item” in SharePoint Designer, the next time you Save and Publish your Workflow, you will inevitably end up with a brand new Custom Content Type.
This can really mess things up when you delete a “To-Do Item” and attempt to re-create it with the same name. You will get an error message stating that the item already exists!
So how do you deal with this problem?
You have to delete the Custom Content Type!!
Unfortunately, this cannot be done directly from the Content Types view in SharePoint Designer, because then you will simply get another error message stating that the Content Type is still in use.
Therefore, the best way to handle this is to navigate directly to the List or Library in SharePoint Designer on which you created the “To-Do Item” and delete it from amongst the listed Content Types.
This should allow you to then re-create the “To-Do Item” with the same name as you desire.