Unable to install Exchange 2013 CU7

Hi,

i hope someone can help me:

i'm unable to install Exchange CU 7

Windows 2012 R2 with Exhcnage 2013 CU5

Event id 6 MSExchange Management

Cmdlet failed. Cmdlet Start-PreConfiguration, parameters -Mode "BuildToBuildUpgrade" -Roles ("LanguagePacks","BridgeheadRole","FrontendTransportRole","ClientAccessRole","UnifiedMessagingRole","MailboxRole","AdminToolsRole","CafeRole").

Event id 2128

Process ExSetupUI.exe (PID=15112). Object DC=Exchange Server was not found on the Domain Controller %4. This may indicate a replication or permission issue. 

Error:

Object reference not set to an instance of an object.

Warning:

An unexpected error has occurred and a Watson dump is being generated: Object reference not set to an instance of an object.

Thanks