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Error: "Not_Set" is an invalid hostname. Please enter a valid hostname

Error Message

When attempting to launch ArcMap, the following error message is returned:

Error:   
"Not_Set" is an invalid hostname. Please enter a valid hostname.
Image of the error message

Cause

The error occurs when a 'Concurrent Use' license level is selected in ArcGIS Administrator, and no License Manager is defined.

Image of the ArcGIS Administrator window showing no License Manager is defined

Solution or Workaround

To circumvent the issue, follow the steps below:

  1. Launch ArcGIS Administrator.
  2. Ensure the correct license level is selected.
  3. If a Concurrent Use license level is selected, click 'Change...' to define a License Manager.
  1. Enter the name of the License Manager in the available field. Alternatively, click 'Browse...' to connect to a specific computer on the network. Click OK.
  1. Click Apply, and OK.
  2. Close ArcGIS Administrator, and relaunch ArcMap.

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