One possible reason why ShellExecute returns SE_ERR_ACCESSDENIED and ShellExecuteEx returns ERROR_ACCESS_DENIED

(The strangely-phrased subject line is for search engine optimization.)A customer reported that when they called ShellExecute, the function sometimes fails with SE_ERR_ACCESSDENIED, depending on what they are trying to execute. (If they had tried ShellExecuteEx they would have gotten the error ERROR_ACCESS_DENIED.) After a good amount of back-and-forth examing file type registrations, a member of