sfTPShellExtensionUI Failed to create Pepare File Operation Dialog

Today I renewed my maintenance licence and upgraded to SmartFTP Client 4.1.1314.0 (64-bit). I am running Windows 7.
I have never had a problem with SmartFTP before but now, whenever I try to upload or download a file I see the following pop-up:
sfFTPShellExtensionUI Failed to create Pepare File Operation Dialog
The log shows:
1. Successful connection to ftp site
2. Successful user log in
...but nothing enters the transfer queue
I am able to view and edit files - when I select a file for editing I can see it enter the transfer queue briefly before it becomes visible in the editor.
Any help greatly appreciated

1. Uninstall any 3rd party software firewall, registry cleaner, antivirus products
2. Delete the registry key at:
https://www.smartftp.com/support/kb/how ... f2625.html
3. Uninstall SmartFTP
4. Delete the c:\program files\SmartFTP Client folder
5. Install SmartFTP