ok as my post in the Beta group reflects, PStools's PSGetSID generates the same errors as kixtart.
This concludes that it is not KiXtart that is generating this problem.
It is the way Windows 7 talks to the AD apparantly.
As my XP clients don't have this problem.
Also, Vista and 2008 (NOT R2) don't have this problem.
I do assume that a Windows 2008 R2 server will have the same problems because it has the same core as Windows 7.