Multicast Image failure

I am trying to start an multicast image but when I hit esc on the server
to start the multicast I get an error: "Could not read image file." I can
image one machine at a time just fine but for some reason cannot start the
multicast process. A CNE stated he thought it was something to do with the
Cisco Switches we have preventing the process. We are running Cisco
Catalyst 3548XL switches.

Novell 6.5.6
ZENWorks 7.0.1 HP5

The workstations attach and gain a multicast address correctly and sit
waiting for the server to start.

Any help would be great!

Rich