You cannot export a licensing report from the Reporting tab on the Licensing page of the vSphere Client.

You click export for a licensing report in the Reporting tab, and the following error message appears:

Cannot export licensing usage data. 
An integrity problem with the license data detected in the database of vCenter Server.

You try to export the license usage for all vCenter Server instances in the Linked Mode group. In the Export License Data dialog box, you select All vCenter Server instances and click Export. The following error message appears:

vCenter Server instances included in the generated export file:
<a list of vCenter Server instance>
Unable to export license usage data for:
<a list of vCenter Server instances>

The license usage data stored in the vCenter Server database was modified. Modifying licensing records in vCenter Server database is discouraged.

The vCenter Server instances for which you cannot export license usage are not running.

The vCenter Server instances for which you cannot export license usage are isolated from the Linked Mode group.

If the license usage data in the vCenter Server database was modified, no solution is available. You cannot export licensing reports for this vCenter Server or Linked Mode group within this time period.

If the vCenter Server instances for which you cannot export a licensing report are not running, restart them if possible and try to export a licensing report again.

If the vCenter Server instances for which you cannot export a licensing report are isolated, restart the vSphere Client and try to export the licensing report again.