Outlook 2010 - Unable to open attachment - "Cannot create file" error

When attempting to open an attachment in an Outlook message you receive the following error:

Cannot create file: Report.xls. Right-click the folder you want to create the file in, and then click Properties on the shortcut menu to check your permissions for the folder.
 
The attachment fails to open. This problem may occur in all file type.

This issue is usually caused when more than 99 attachments with the same name have been opened.
When attachments are opened they are saved into a temporary folder (e.g. 'Report.xls'). If the file name is already in use, it will save it as 'Report(1).xls', As more files are opened it will continue to create new files until it gets to 'Report(99).xls' after this it will be unable to create any new files and will fail to open any attachments with the file name of 'Reports.xls'.

To resolve the issue you will need to delete the files in the temporary folder. The path to this folder changes depending on which version of Windows and Office you have installed. You will need to check the registry to get the folder path. Before proceeding you should close Outlook Application

Open the registry editor (Start -> regedit). Navigate to the path below for your version of Outlook

Outlook 97	HKEY_CURRENT_USER\Software\Microsoft\Office\8.0\Outlook\Security
Outlook 98	HKEY_CURRENT_USER\Software\Microsoft\Office\8.5\Outlook\Security
Outlook 2000	HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security
Outlook 2002/XP	HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security
Outlook 2003	HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
Outlook 2007	HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security
Outlook 2010	HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security

Open the 'OutlookSecureTempFolder' registry key and take note of the path. Navigate to the folder path. Delete the duplicate files (or all files) in the folder