mailbox migration failing after Upgrading CU5 -> CU6

hello fellow readers,

we have an Exchange 2007 (latest needed Patchlevel) / Exchange 2013 CU6 Environment and are now having trouble migrating user mailboxes from the Ex2007 mailbox server to the new Ex2013 server.

migration of the first boxes before applying CU6 went fine and smooth, but now all mailbox moves are stuck with the status "Qeued".

a ps command "get-moverequeststatistics karl.treiber" brings the following

Postfach 'Karl Treiber' wird zurzeit nicht verschoben.    + CategoryInfo          : InvalidArgument: (karl.treiber:MoveRequestIdParameter) [Get-MoveRequestStatistics], Mana   gementObjectNotFoundException    + FullyQualifiedErrorId : [Server=SERVERNAME,RequestId=bf51511d-c7b8-4b39-ad60-caa71015cc6c,TimeStamp=10.11.2014 11   :27:29] [FailureCategory=Cmdlet-ManagementObjectNotFoundException] 9B1AC428,Microsoft.Exchange.Management.Recipien  tTasks.GetMoveRequestStatistics    + PSComputerName        : SERVERNAME.DOMAIN.local

i'm guessing that this is correct, as the migration hasn't started yet. in somehow similar threads people suggest putting the BadItemLimit higher, so i tried running ps command "set-moverequest karl.treiber -baditemlimit 9999" bringing the following

ARNUNG: Wenn ein Element nicht aus der Quelldatenbank gelesen oder in die Zieldatenbank geschrieben werden kann, wird
es als beschädigt betrachtet. Wenn Sie für 'BadItemLimit' einen anderen Wert als Null angeben, fordern Sie an, dass
Exchange diese Elemente nicht in das Zielpostfach kopiert. Nach Abschluss der Verschiebung sind diese beschädigten
Elemente nicht im Zielpostfach verfügbar.
Der Vorgang konnte nicht ausgeführt werden, weil keine Objekte des Typs
'Microsoft.Exchange.MailboxReplicationService.TransactionalRequestJob' auf 'DC.DOMAIN.local' gefunden wurden.
    + CategoryInfo          : NotSpecified: (:) [Set-MoveRequest], ManagementObjectNotFoundException+ FullyQualifiedErrorId : [Server=SERVERNAME,RequestId=ab82c24b-7914-4382-8de2-34462d4993b3,TimeStamp=10.11.2014 11
   :38:01] [FailureCategory=Cmdlet-ManagementObjectNotFoundException] 285DB966,Microsoft.Exchange.Management.Recipien
  tTasks.SetMoveRequest+ PSComputerName        : SERVERNAME.DOMAIN.local

my guess is, that something is missing in AD - but what? DC replication is checked and working as normal. i looked up the AD object of the user, searchung for Exchange values, finding some connecting to mailbox moves, but none similar to "Microsoft.Exchange.MailboxReplicationService.TransactionalRequestJob".

everything worked in CU5 -> after updating to CU6 we had serious issues with mailbox databases in dirty shutdown and called MS or help. as mentioned here this was a known error and they gave us the hotfix for that. the hotfix seemed to be so "hot" that it fixed the database problem but brought new ones, as the fix seems to not check Exchange installation path, assuming its always c:\Program Files\... (which it is not in our case).

here they suggest to run "setup /preparedomain" again, but i am worried about possible new problems.

has anyone suggestions what to check?