Answer

PROBLEM 

The navigation tree on the left in the Web UI is blank. This problem might also affect other parts in the UI. 

In the logs, you might find errors similar to:
 

ENVIRONMENT

• GFI MailEssentials
• All supported environments

SOLUTION

Ensure the NETWORK SERVICE account has full access to the affected temp folder; in this case C:\Windows\TEMP\:

1. Browse to the Temp folder, right click it and select Properties
2. Click the Security tab
3. Click the Edit button
4. Click the Add... button
5. Enter NETWORK SERVICE and click OK
6. With the new NETWORK SERVICE entry under Groups or user names selected, tick the Allow box for Full Control
7. Click OK, then click OK again back on the Properties window

CAUSE

Missing permission on the temp folder.