Machine Already Discovered error when attempting to discover a server

When attempting to discover a machine, the discovery job fails with a message stating that the machine has already been discovered.

This message is likely to occur if any of the following scenarios is true:

• The machine contains a network adapter (or similar hardware device such as a Remote Access Card)
  that contains the same MAC address of a machine that has already been discovered
• The machine being added was previously discovered under a different hostname
• The machine being added was previously discovered under a different Domain/Workgroup

To resolve the issue, remove the previously added machine entry before attempting to re-discover the desired machine.