Update feature for plugins, themes and WordPress

I’m having a little trouble with the update feature in WordPress.

I upgraded to WP 3.5.1 a little while ago using the update feature with no problems at all. I also updated several plugins at the same time.

Since then, I’ve not been able to update any plugins or themes from within WordPress itself. The only way I can do it is to FTP each one which is incredibly time consuming.

When I try to install a new plugin from within WP, I get the following error message:

Installing Plugin: MobileView by ColorLabs & Company 1.0.7

Downloading install package from http://downloads.wordpress.org/plugin/mobileview.zip…

Unpacking the package…

Could not create directory. /home/stormy/public_html/wp-content/upgrade/mobileview.tmp

Return to Plugin Installer

And if I try to update an existing theme/plugin, I get this message:

The update process is starting. This process may take a while on some hosts, so please be patient.
Updating Theme Adventure (1/1)

Downloading update from http://wordpress.org/extend/themes/download/adventure.2.2.zip…
Unpacking the update…

An error occurred while updating Adventure: Could not create directory. /home/stormy/public_html/wp-content/upgrade/adventure.tmp.

All updates have been completed.

Return to Themes page | Return to WordPress Updates

Can someone please give me an idea as to why this feature is not working now? I would update from within WP using FTP but it does not prompt for credentials.