Try checking on switch setting as well. What is the switch model used? have you tried connecting to another brand of switch for testing? Used to encounter issue unable to connect even when using static IP. Tried changing the connection to another switch then it worked. Not sure if this is applicablicable to your case..
The most likely cause for this issue is a link failure during the LUN connection phase. This could be caused by speed/duplex missmatch, faulty cable, or switch port issue. Make sure the switch port is set to Autonegotiate. If it is already set to Auto, then swap out the cable with one that has known to work in the past. If the issue still persists then can you try another switch port?
If this is a dual port NIC, you can try to assign the other port as "secondary" in the iSCSI boot configuration screen. If you see a message that the secondary port is being used then that would tell us that there is something wrong with the primary port, cable, or switch port.