One of our branch offices has an ISA 2004 proxy server which connects them to the internet. Whenever a Mac user tries to download a large (larger than 20MB or so) file via FTP, the file corrupts. Mac users use FetchFTP and connect to the ISA SOCKS4 proxy on port 1080. PC users in the same office have the ISA firewall client installed (connecting over port 8080) and can download the same large files without any issue.
I have tried pointing a Mac client in the branch office at our local TMG 2010 proxy server (on SOCKS4 port 1080) and I can download large files no problem. if I point one of our local Macs at the branch ISA 2004 proxy I get the corruption issue. So the issue is definitely to do with the SOCKS4 proxy on ISA 2004. SP3 is installed with the latest patches. Any available Windows update is installed. There are no settings I can see within ISA 2004 which I can change which might fix the issue.
Does anyone have any ideas what we could do to fix the problem?
