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WordPress Update Fails: The update cannot be installed because we will be unable to copy some files

August 20, 2018

While updating a WordPress site hosted on a Windows platform (Internet Information Server); I came across this error:

The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.: wp-admin/includes/update-core.php

I confirmed the Application pool identity for the site had the appropriate permissions. After some reading related to the same error on an Apache web server I found the issue possibly due to the Read Only flag on some files or folders within the WordPress install folder.

I used the Windows property manager to ensure the Read Only flag for all files is UNCHECKED:

Cascade the setting to subfolders and files: