This problem is all over my district:

Zen7 sp1 hp6
Netware 6.5 sp6

Zen Imaging works, but ---

We can only pull down images to 4 pcs at at time else all *imaging
slows down to crawl and/or times out.*

Also multicasting will work, but will only pass out a session number to
4-5 clients. *Clients 6 and up never get a session number, and
therefore never receive the image.*

Spanning tree, and Fast Start, is enabled on all switches. The core is
a Gigabit core.

We did move DHCP service onto the same server as Zenworks, and followed
the instructions on TID 3808002. DHCP is working fine. Option 60
enabled, Option 43 not enabled.

Any Ideas?? This is a very serious problem.