XG Web Proxy - problem with ftp site published behind UTM

Hi All,

I have a FTP site published by a UTM server.  It's a standard simple FTP site, directory browsable by Internet Explorer.

I can connect to this site successfully anywhere - except through a XG Firewall web proxy.  If I try, I get the following dialog box..

"Do you want to open or save <ip_of_ftp_site>/ from <ip_of_ftp_site>?"

I took a look at the web proxy logs - nothing appears to be blocked.  Other FTP sites (like the university of kent mirror sites) work successfully.  The only difference is that the destination site lies behind a UTM firewall.  If I try to access the site using a UTM web proxy, it works fine.

Anyone have any ideas?  I'm scratching my head on this one...