I have encountered the User cannot be found error a few times when accessing the List Settings or Library Settings . Solution: To republish the workflows you can follow the next steps: Open your site in SharePoint Designer 2010 Click on the Workflows link from the Site Objects menu Click on the workflow name, this will open your workflow Click on the Publish button Do step 3 and 4 for all the workflows. Go back to your List or Library Settings and the error should be gone.
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