Check for Updates fails via Webroot web proxy service

In version 4.2.5, the Check for Updates option fails for me with one of two errors:

Socket error (No connection could be made because the target machine actively refused it)

or

Received response 404 Not Found from localhost

The first error occurs if I select 'No proxy', and the second error occurs if I select 'Automatically detect proxy settings', or if I set them manually.

We use a hosted web proxy service called Webroot which sets proxy settings on our PCs to point to localhost with port 3128. I suspect that the WinSCP update server doesn't like our web proxy service. Is there anything that can be done to resolve this, other than bypassing our web proxy service for updates?

Can you send me an email, so I can send you back a debug version of WinSCP to track the problem? Please include link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.