KB Article: http://support.microsoft.com/kb/321186

INTRODUCTION

If you double-click a drive or folder, Search Companion may start and the drive or folder may not open. If you configure settings for other actions that are associated with drives or file folders (for example, Open Command Window Here or Print Directory Listing), Windows may perform one of these actions instead of starting Search Companion.

NOTE: If you configure the Single-click to open an item (point to select) setting in Windows, this problem may occur if you single-click a drive or folder.