Unattened W7 join domain stopped working

We had a working WDS setup to install our clients but for some reason the part where the computer should join the domain it fails

<component name="Microsoft-Windows-UnattendedJoin" processorArchitecture="x86" publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <Identification>
  <JoinDomain>ourdomain.loc</JoinDomain>
  <UnsecureJoin>true</UnsecureJoin>
 </Identification>
</component> 

No changes to the unattend files or the WDS server has been made. The join domain issue also fails on another WDS server located on another site. So it must be something centralized - and the only thing I can come up with is our Active Directory.

But I have no idea what to look for. (the only resent change is that we added a ReadOnly Domain Controller, but this RODC is on another network)

The error we get in the setupact.log file is

2013-03-15 12:09:54, Info                         [DJOIN.EXE] Unattended Join: Checking that auto start services have started.
 2013-03-15 12:09:54, Info                         [DJOIN.EXE] Unattended Join: Joining domain [ourdomain]...
 2013-03-15 12:09:54, Info                         [DJOIN.EXE] Unattended Join: Calling DsGetDcName for ourdomain...
 2013-03-15 12:09:54, Info                         [DJOIN.EXE] Unattended Join: DsGetDcName returned [DOMAINCONTROLLER_NAME]
 2013-03-15 12:09:54, Info                         [DJOIN.EXE] Unattended Join: Constructed domain parameter [ourdomain\DOMAINCONTROLLER_NAME]
 2013-03-15 12:10:06, Warning                      [DJOIN.EXE] Unattended Join: NetJoinDomain attempt failed: 0x6be, will retry in 5 seconds...
 2013-03-15 12:10:11, Warning                      [DJOIN.EXE] Unattended Join: NetJoinDomain attempt failed: 0x85a, will retry in 5 seconds...
 2013-03-15 12:10:16, Warning                      [DJOIN.EXE] Unattended Join: NetJoinDomain attempt failed: 0x85a, will retry in 5 seconds...
 2013-03-15 12:10:21, Warning                      [DJOIN.EXE] Unattended Join: NetJoinDomain attempt failed: 0x85a, will retry in 5 seconds...

If I specify a user (domain admin) to join the domain everything works fine. (using secure domain join)

 <Identification>
 <JoinDomain>our_domain</JoinDomain>
  <UnsecureJoin>false</UnsecureJoin>
   <DebugJoin>true</DebugJoin>
    <Credentials>
     <Domain>our_domain</Domain>
     <Password>our_password</Password>
     <Username>our_domainAdminUser</Username>
  </Credentials>
</Identification> 

Any suggestions how to resolve this?

(there is no problem adding the computer to the domain manually.)