This is a bit of hardware issue but it's affecting our ZEN image

Our Zen (Linux) client will not connect to our Zen (Netware) server from
PIX boot, only on certain ports. On investigation it appears that
connections into the core switch (Procurve 5308) will not connect, but
connections into a different switch (Procurve 2524) work fine.

Windows will connect to either of these servers from either of these

The obvious swaps between ports has been made, i.e. same PC to different
switch, and the problem follows the switch.

What needs to be adjusted on the switch for this to work?

Any suggestions gratefully received.