[Samba] How to properly demote a W2003 from Samba4?

[Sam]

Hello all,

I'm always trying to migrate from W2000 server to Samba 4.

For doing this, I tried this :
- install a W2003 server with AD and DNS services, join it to W2000, 
transfer roles and after demote the old W2000 -> done
- install a Sernet Samba4 with Bind9, join W2003, transfer roles -> done

At this point the sync process is working in two way, I can manage DNS 
and AD with rsat tool even directly on the Samba4 server... Which was 
hard to do this to work properly! ;)

Now I can't demote the W2003 server, the only way I find is to use 
"dcpromo.exe /froceremoval" command... ( the alone "dcpromo.exe" command 
don't work... )
But now Samba4 always trying to contact the w2003 server and I can't 
clean the dns and active directory, I've some error for example in 
"domain controllers" section of the AD...
if I try "samba-tool domain level raise --domain-level=2008_R2" I read 
"ERROR: Domain function level can't be higher than the lowest function 
level of a DC!"

So how to do a clean demote process even manualy? ( I can't set up a 
fresh new AD because I have too many users profile to move...)

Thanks for helping! :)

Samuel