I ran into an issue today with a site which had recently been upgraded.
The customer reported that the preview didn't work any more.
I did some googling and I found a thread on Our Umbraco which was marked with a solution, but the solution which actually worked for me was further down.
The solution was to delete the folder
Umbraco > Preview
The reason for this is because in the upgraded version of Umbraco the files have been moved to the new folder:
Umbraco > Views > Preview
So by deleting the old folder it solves the issue.
Thank you to Paul Wright for posting this solution #h5yr
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