1. Close Outlook
2. Go to Start > Control Panel > Add or Remove Programs (Programs and Features in Windows 7). 
3. Uninstall GIFTS Online Link to Outlook plugin. 
4. Also uninstall the following Outlook Add-In items, if present: 
Microsoft Office 2003/2007/2010 Primary Interop Assembly 
Visual Studio 20xx Tools 
5. Restart your computer 
6. After rebooting, open Outlook and make sure the above Add-Ins have been removed
Outlook 2003: Tools > Options > Other > Advanced Options > Add-In Manager 
Outlook 2007: Tools > Trust Center > Add-Ins 
Outlook 2010: File > Options > Add-Ins 
7. Close Outlook. 
8. Install the plugin again