Try to restart the AIX system then try once more to connect, I found a case about 2.5 yrs ago where this worked for one customer.

Another idea is to match the iSCSI Daemon options from the Console to the AIX system.


Go to the console tools:
Ctl-Alt-W
Select Tuning Options
Select iSCSI Daemon options
Select Target Options
Select a target
match all to the host for things like MaxRecvDataSegmentLength and MaxXmitDataSegmentLength.