I have recently run into problem that my Vista Business did not allow to select multiple files located in particular folder when using Windows Explorer.
It was not possible to select more than single file by keyboard shortcuts nor with using Ctrl + mouseclick or Shift + mouseclick.
To fix it I needed to delete registry key located in:
HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags
This key contains mutliple subkeys where indivdual settings for each folder are saved. Because I could not identify this particular folder settings so just deleted all of them that they returned to factory settings.
Later I found in Microsoft Knowledge Base solution which does not require manual editing of registry: http://support.microsoft.com/kb/934548/en-us