To first resolve this problem obviously you need a domain controller in the same site as the Exchange 2010 server you are trying to install.  It must also be a global catalog.  Both of these items can be configured via the active directory sites and services snap in.\nIf y0u have verified that simply use the command line to initiate your install point setup.com to the correct AD server.\nsetup.com /mode:install /role:mailbox /dc:DCinMYsite