Try this from our FAQ:
The ClearContext Add-in has become disabled (or is not loading), how do I re-enable?
If Outlook terminated during operation, the ClearContext add-in could be disabled. The first step is to restart Outlook and see if that fixes the problem. If this does not work, follow the instructions below to re-enable:
1. In Outlook 2003 and 2002 (XP), Select Help > About Microsoft Outlook > Disabled Items and select the checkbox next to add-in:clearmail.dll.
2. If this doesn't work, in all Outlook versions, Select Tools > Options > Other > Advanced Options... > COM Add-Ins... and ensure the box next to ClearContext is checked.