[Samba] Samba AD - Unix attributes problem

[Aqz]

Hi,

I've recently started using Samba4 (Sernet binary, 4.0.16 on Centos 6) as
PDC.
I would like to assign unix attributes using MMC console "Active Directory
Users and Computers" however every time I'm trying to do this I get an
error "Unable to modify the object property values. Check your credentials.
There could be a network problem blahblahblah"..

I've provisioned domain using "--use-rfc2307" option.

What am I missing here?

-- 
Wojtek