Try each of the following steps in order until the issue is resolved:
  1. Log into the server with a local administrator account.
  2. Manually unregister and then register the SQLDMO.dll file located in C:\Program Files\Microsoft SQL Server\80\Tools\Binn\.   If the SQLDMO.dll file is not present, then install the SQL Server 2005 Backwards Compatibility Components.
  3. Run the Setup.exe from the CD or downloaded installation file and choose Repair.