Classic Gotcha - Configuring a Freenas

From the freenas documentation:
http://www.freenas.org/images/resources/freenas8.2/freenas8.2_guide.html#1.6.3.6.Creating a zvol|outline

The standard configuration for a iSCSI target for XenServer (I configured one with v6.0) doesn't work - when trying to connect you get an authentication error (the standard one you get if you have missttyped a CHAP password).
This is even if authentication is turned off.
In section  freenas8.2_guide - 8.7 Target Global Settings, the following settings are 'recommended' for Xenserver:

Before modifying any integer values, refer to the iSCSI initiator's documentation. For example, the following modifications are recommended if the iSCSI initiator is running on Xenserver:

• Max. pre-send R2T: 255
• MaxOutstandingR2T: 64
• First burst length: 262,144
• Max burst length: 2,097,152