The situation: We need to create a duplicate of a site with Nintex Forms and Workflow. We accomplish this by creating a new site based on a Export-SPSite .CMP file and importing the required Nintex workflows through PowerShell.
The Issue: When we try to deploy exported Nintex workflows to the duplicate site we get the following error: A workflow with this name already exists on the site. This is despite there being no workflows displaying on the “Manage Nintex Workflows” pages of any of the lists or libraries in the site.
The Solution: This issue is caused by the .CMP file still containing workflow association data, even while the workflows themselves were not carried across with the site export. There is a hidden library in every SharePoint site that contains the Nintex workflow association data. You can access this library via the this address http://YourSite/NintexWorkflow/. If the corresponding folders are deleted, the workflows will deploy without issue.