SharePoint 2013 workflow HTTP Unauthorized error

I was able to create and publish a 2013 workflow. I created a simple workflow that only added comments to the workflow history. So it should work… but I kept getting this error:

HTTP Unauthorized to http://sitename/_vti_bin/client.svc/web/lists/getbyid(guid’guid’) Correlation Id: id Instance Id: id

I tried everything. After going thru the logs I noticed an error .pdf” is not checked out.  You must first check out this document before making changes.

So I disabled “Require Check Out to edit” and workflow was able to update the status and completed successfully