Hi Julien,
Thanks for coming back to me. Looks like you are on the right path with your diagnosis. I logged a case with DELL and they checked the Equallogic and the switches. They said the Equallogic looked fine as it is presenting itself to the hosts. However they think there is a loop in our network as the switch logs are flooded with these messages
<189> JUL 26 08:10:04 192.168.42.48-1 TRAPMGR[151077744]: traputil.c(611) 647 %% 2/0/1 is transitioned from the Forwarding state to the Blocking state in instance 0
<189> JUL 26 08:10:04 192.168.42.48-1 TRAPMGR[151077744]: traputil.c(611) 648 %% 2/0/2 is transitioned from the Forwarding state to the Blocking state in instance 0
I don't know much about the switch config other than what the engineer sent through after the configuration was completed.
Either way I'll read the document you sent through and speak to DELL to see how we can fix the problem.
Thanks again for your help 
Lee