[Samba] problems with msdfs proxy in AD environment

[Andrea Lorenz]

Hello,

we have two solaris file servers which export the file with nfs to the 
unix client and with samba to the windows clients. Both file servers are 
member of an active directory domain.
Now we have the idea to use a new samba file server which contains the 
shares of both file servers and redirect the request to the correct file 
server with msdfs proxy.
On this new fileserver I configure
[global]
   ...
   encrypt passwords = Yes
   lanman auth = no
   ntlm auth = no
   client ntlmv2 auth = yes
   workgroup = xxx
   security = ads
   realm = XXX.RZ.RWTH-AACHEN.DE
   password server = xxx.rz.RWTH-Aachen.DE
   host msdfs = yes
[homes]
   msdfs proxy = \yyy.rz.rwth-aachen.de\homes
   browseable = no

I can connect to the homes share from a windows client which is not a 
member of the AD. But if I use a windows client which is member of the 
domain I get the error message
   "The drive could not be mapped because no network was found"

What could be the reason?

We use samba 3.0.23a without winbind. The unix and the windows site have 
  different user administrations. The samba users have the same account 
name on both systems.

Thanks in advance,
Andrea