Adprep could not discover the Naming FSMO. The Naming FSMO must be discoverable for this operation to proceed. Status/Consequence ...

Adprep could not discover the Naming FSMO. The Naming FSMO must be discoverable for this operation to proceed. 
[Status/Consequence]
Adprep could not complete the operation.
[User Action]
Check the log file ADPrep.log in the %1 directory for possible cause of failure.