Default FastSCP isn’t working with ESX 3.5. I just noticed this download: http://www.veeam.com/download/fastscp/FastSCP.xml
It’s indeed a firewall related problem, copy this file into /etc/vmware/firewall.
Run the following command “service mgmt-vmware restart” and open up the Portrange with VirtualCenter. Opening it up can also be done from the commandline with “esxcfg-firewall -e FastSCP”. Veeam still has to fix the “edit function” which doesn’t work with 3.5 anymore, expect a new release in Januari / Februari 2008.