Get-ADDomainController : Directory object not found

No, I don’t have a solution to the above. But I do have a workaround in case it affects any one else. :) 

ldifde -d "OU=Domain Controllers,DC=contoso,DC=com" -f c:\output.txt -l "sAMAccountName, operatingSystem" -r "(&(objectClass=computer))"

Of course replace “contoso” and “com” with your domain specific names. 

Update: It could be related to Riverbeds or any other WAN Accelerators you may have. Check this thread.

Thanks to a colleague, a PowerShell based workaround is the following:

(Get-ADDomain -Identity 'contoso.com').ReplicaDirectoryServers | ForEach { Get-ADDomainController -Identity $_ -Server 'contoso.com' }

This gets a list of the read-write domain controllers and runs the Get-ADDomainController cmdlet against each of them.