Should Client Access be configured to use Kerberos? If Kerberos is not implemented then it is not possible to use that option.
On the Client Access session click ‘Communication’, ‘Properties’, in the ‘User ID signon information’ field doe it have ‘User Kerberos prinicpal name, no prompting’?
If it does try changing it to ‘Use default user ID, prompt as needed’ and add the required ID in the ‘User ID’ field.
The User’s Guide that installed with iSeries Access lists error messages. You should look there before going out to a forum.
The User’s Guide has this:
The iSeries server connection is configured to use your Kerberos principal name for security authentication. These credentials were not found on your workstation. For Windows workstations, you need to log on to a Windows 2000 or XP domain, in order to obtain Kerberos credentials.
Log off your workstation. Log back onto your workstation, and provide the appropriate domain name.
Have you followed those instructions?