Da hast du Recht, CA ist nicht erforderlich, aber:

There is also a known NTLMv2 authentication problem in NetServer that was fixed awhile ago that could affect Windows 7 connections, as well as connections from other Windows OS versions. While the APAR description (MA37975) is fairly specific, the fixing PTF should be on any IBM i where NTLMv2 issues of any kind are suspected.

V5R4M0: MF47178
V5R4M5: MF47174
V6R1M0: MF47172
V6R1M1: MF47173

es scheint daher keine Problemlösung vor V5R4 zu geben!