What is your build of DSS that you are using?

It could be that you need some tuning, try :

maxRecvDataSegmentLen=262144
MaxBurstLength=16776192
Maxxmitdatasegment=262144
FirstBurstLength=65536
DataDigest=None
maxoutstandingr2t=8
InitialR2T=No
ImmediateData=Yes
headerDigest=None
Wthreads=8

Also to change the Jumbo frame:
http://kb.open-e.com/Does-Open-E-sup...Frames_28.html

This changes should be made to each target.

Try also to check your initiator settings, even if you have to remove all settings and create them again.