EMC error: An error caused a change in the current set of domain controllers.

When opening Exchange Manangemnt Console you get the following error: An error caused a change in the current set of domain controllers. It was running the command āGet-OrganizationConfigā. In the application log you get the following error entries: Event ID: 4 Source: MSExchange Configuration Cmdlet ā Remote Mamagment General: Task Get-ExchangeServer writing error when processing record of index 0. Error: Microsoft.Exchange.Data.Directory.SuitabilityDirectoryException: An Active Directory error 0x51 occurred when trying to check the suitability of server ādc.mydomain.comā. Error: āActive directory response: The LDAP server is unavailable.ā ā>