[Samba] Replication error after trying to sync sysvol

[Johannes Amorosa | Celluloid VFX]

I tried to synchronize the sysvol folders, on two dcs. Something went 
wrong since yesterday we have replication problems:
One machine shows this, while the other one is happy.

samba-tool drs showrepl

==== INBOUND NEIGHBORS ====

DC=DomainDnsZones,DC=ourdomain,DC=com
     Default-First-Site-Name\DC03 via RPC
         DSA object GUID: af610e1a-9e3b-4cdd-a36b-c296d77a9479
         Last attempt @ Fri Mar 27 12:58:42 2015 CET failed, result 121 
(WERR_SEM_TIMEOUT)
         126 consecutive failure(s).
         Last success @ Fri Mar 27 03:40:24 2015 CET

DC=ForestDnsZones,DC=ourdomain,DC=com
     Default-First-Site-Name\DC04 via RPC
         DSA object GUID: af610e1a-9e3b-4cdd-a36b-c296d77a9479
         Last attempt @ Fri Mar 27 12:51:41 2015 CET failed, result 121 
(WERR_SEM_TIMEOUT)
         102 consecutive failure(s).
         Last success @ Fri Mar 27 03:40:24 2015 CET

DC=ourdomain,DC=com
     Default-First-Site-Name\DC03 via RPC
         DSA object GUID: af610e1a-9e3b-4cdd-a36b-c296d77a9479
         Last attempt @ Fri Mar 27 12:57:42 2015 CET failed, result 121 
(WERR_SEM_TIMEOUT)
         106 consecutive failure(s).
         Last success @ Fri Mar 27 03:40:25 2015 CET

CN=Configuration,DC=ourdomain,DC=com
     Default-First-Site-Name\DC03 via RPC
         DSA object GUID: af610e1a-9e3b-4cdd-a36b-c296d77a9479
         Last attempt @ Fri Mar 27 12:53:41 2015 CET failed, result 121 
(WERR_SEM_TIMEOUT)
         102 consecutive failure(s).
         Last success @ Fri Mar 27 03:40:26 2015 CET

CN=Schema,CN=Configuration,DC=ourdomain,DC=com
     Default-First-Site-Name\DC03 via RPC
         DSA object GUID: af610e1a-9e3b-4cdd-a36b-c296d77a9479
         Last attempt @ Fri Mar 27 12:54:41 2015 CET failed, result 121 
(WERR_SEM_TIMEOUT)
         102 consecutive failure(s).
         Last success @ Fri Mar 27 03:40:28 2015 CET
<snip>

Every service still seems to work - but we're quite nervous - this is a 
production system(lesson learned!).

I tried to force sync
samba-tool drs replicate --full-sync DC04 DC03 dc=ourdomain,dc=com
ERROR(<class 'samba.drs_utils.drsException'>): DsReplicaSync failed - 
drsException: DsReplicaSync failed (-1073741643, 'NT_STATUS_IO_TIMEOUT')

Or setup:
sernet-samba                             99:4.1.17-10

[global]
     workgroup = OURDOMAIN
     realm = OURDOMAIN.COM
     netbios name = DC04
     log level = 3

     server role = active directory domain controller
     dns forwarder = 192.168.1.254
<snip>

Ubuntu 12.04

How can I fix this. Any help is highly appreciated.
Joe

-- 
Johannes Amorosa | Celluloid VFX