This problem is specific to Outlook 2003 users.You may find that Norton Antivirus removes the Clearvale It executable file as it deems it a risky file. To restore this file:

Open the main Norten window and click the Quarantine link.
In the Quarantine window, select the Clearvale It executable fi...(More)

If you are using Outlook 2007 or 2010, Clearvale It uses Microsoft ClickOnce to manage the installation and updating of the Clearvale It add-in.If the ClickOnce cache is not correctly cleared, the ClickOnce installer might display a message that the latest version is already installed.Solution1.&nbs...(More)

Here are some possible reasons why the Clearvale It button does not appear:

Conflict with another Outlook add-in.
The Outlook process hung while executing some add-in code.
Unhandled exceptions in the add-in code.

Solution
Try to re-enable the Outlook add-in from the disabled items.
Outloo...(More)