PS6000 showing packet errors but no errors appear on the switch

PS6000 showing packet errors but no errors appear on the switch

We have a loaned PS6000E SAN that we are using to relocate our iSCSI LUNs
off our current PS4000E SAN to upgrade it from Seagate Moose drives under
a proactive replacement plan by Dell. We've connected it up to our stack
of Dell PowerConnect 6248 switches that make up our client stack (because
our Cisco stack is currently full - another is on order so we can extend
it and give our server network room to grow) and while it connects to our
existing stack and we've successfully moved a LUN across, there are
numerous errors on the Ethernet connectors that are giving us cause for
concern.
Our other two SANs are connected to our Cisco stack and show no errors at
all. They connect to the Dell stack via a fibre link which does not have
jumbo frames turned on.
We are not particularly keen on moving across the remainder of the LUNs
until we resolve this issue. Is there something on the switch we need to
configure that I'm missing? Should I not be using the PC6248s for this and
should I wait for our new Cisco switch to arrive? Am I getting myself into
a fuss over nothing?
EDIT: I noticed spanning tree was turned on for the ports and turned off
for the SAN ports on the Cisco switch. Turning it off has done nothing to
stem the errors coming from this thing. I ensured that the MTU was 9000
across the board and it hasn't made a difference. All cables are CAT6.
Turning off LLDP made no difference. Someone requested a diagram, which is
below.