Symptoms
When you try to activate Workflows site collection feature you may get the following error message:
"A list, survey, discussion board, or document library with the specified title already exists in this Web site. Please choose another title."
Solution
1. Download and install SharePoint Designer 2013.
2. Start SharePoint Designer and connect to the problem site.
Please note: Site Collection Administrator permission is required.
3. Under 'All Files'/_catalogs find wfpub folder and rename it.
3. Open problem site in the browser and navigate to Site Settings⇒ Manage site collection features
4. Activate Workflows feature.
5. Deactivate Workflows feature.
6. Activate the Workflows feature again.