When you try and install Smoothwall updates, the system briefly displays a window showing that files are being downloaded, before telling you that updates cannot be installed. Even if you reboot the system, you still cannot install updates or new releases.
The cause is usually related to the update cache and the installation of previous updates.
To check that you are affected by this issue, connect to the Smoothwall unit using PUTTY. By default, the SSH port to connect to Smoothwall systems is port 222.
You will then be able to install updates, usually without requiring another reboot.