FTP and ISA 2004
SBS 2003 SP1 Premium includes ISA 2004. After upgrading to SP1, I discovered that I could not do an FTP upload from any workstation - it was failing with a 500 access denied error.
Here's the fix:
On your SBS server, open up ISA Server Mgmt, click on Firewall Policy, and scroll down and locate the policy labeled 'SBS Internet Access Rule'. Right click on this rule, and then click on the option 'Configure FTP'.
In the popup window that opens, click to UNCHECK the 'read only' option, then click Apply, then OK.
THEN --- look towards the top of the ISA Firewall Policy window, and you will see two new buttons displayed: Apply and Discard. Be sure to click on Apply, otherwise the changes you just made will NOT be applied.
Go back to your workstation, restart your FTP client utility and happy uploading!