Ok, WordPress has a great feature built in these days which helpfully tells you when an upgrade is available and gives you the ability to upgrade automagically via ftp through the admin backend.
9 times out of 10 this will work without hitch, however today I came across one install that just wouldn’t work at all. For some reason, WP was unable to copy all the required files to a temporary directory on the server in order to complete the upgrade.
Basically this is a very quick fix, so if you have the same issue, hopefully this will help:
Change the permissions on folder ‘wp-content/upgrade’ to 777.
Re-run the installer.
No really, it’s that simple.
Don’t forget to change to 755 on the above folder when install is complete.