Sometimes people will be unfortunate enough to find themselves with no choice other than hosting WordPress on a Windows server. This is all kinds of horrible, as anyone who has every tried to do this will know that Windows permissions are an absolute pain in the ass. Things like auto-upgrading WordPress become a nightmare. Most of the time it’s just easier to FTP or copy the files over the top of the old ones.
But those days are over! There is a magic bullet where with one simple change, WordPress will stop throwing errors on upgrades as well as plugin updates. Lovely.
Simply grant the IUSR full control of your WordPress directory.
So, locate the directory and right click it. Hit properties, then pick the security tab. Click Edit. If IUSR is already there, just select it and hit the Full Control tick box and accept. Do not get confused with the IUSRS group, and the IUSR is not in there! If you can’t see IUSR, hit ‘Add’ and enter “IUSR” without the quotes. Hit OK, make sure the new user is selected and click the Full Control tick box. Apply it and you’re done.
Update: Note that if you are using Plesk Panel to manage your web server, you will also need to grant the same permissions for ‘Plesk IUSR’ and ‘Plesk WP User’ for that domain. And when you get a chance, dump the horrible bit of software that is Plesk panel as well as any other software you are using which is developed by Parallels!