Unpacking the update | Installation Failed | FIX

This is an answer to anyone who has received this error message:

Downloading update from http://wordpress.org/wordpress-X.X.X.zip…
Unpacking the update…
Could not copy file.: /home/xxx/public_html/wp-content/upgrade/wordpress-3.tmp/
Installation Failed

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These fixes work with all versions:”

Things to check.
-:- Permissions: wp-content/upgrade folder should be 755, although I see some suggesting 777 if you are having problems. If you do change to 777, change back to 755 after successful update.
-:- File: wp-content/upgrade make sure the folder is empty. There may be old upgrade files that can simply be removed.
-:- Disk Space* – make sure you have sufficient FREE space to enable the update. The update uploads a complete WP File (4.5Mb), then unpacks it (another 4.5Mb), sends a copy of the updated files (possibly another 4.5Mb) which overwrites the neccesary files, then it removes all used files) and reports a successful upgrade. If you do not have sufficient space, it will report
Unpacking the update…
Could not copy file: wordpress-3.tmp/
Installation Failed
-:- Memory – I have seen some suggestions that there may be memory issues, but my logic would be if you had enough memory to do an install in the first place, then you probably have enough memory to do an update. If the suggestions above don’t work, I reckon if its a memory problem then the error message will be different.

* This turned out to be my problem

Hope it helps everyone. It worked for me.
Ripefruit