I'm trying to run a multicast image session and it isn't going well.

I'm running NetWare 6 and Zen 6.5.

I have a lab of ~60 machines which are imported. I setup a multicast
session for all of them but when I restart the machines the ones that
join early seem to work fine but after "X" number (this last time it was
10) machines stopped joining. During the PXE boot they thought that
there was no work to do and booted normally. My session was set for 60
machines to join or 5 minutes elapsed. After some time elapsed the
multicast session started.

Any ideas? The machines are connected via 100Mb and the server has a
1Gb card. That server also runs iFolder FWIW.