There was an error when attempting to upgrade the existing portal. com.esri.arcgis.portal.admin.core.site.migration.MigrationException: Failed to upgrade the PostgreSQL from 9.6.8 to 10.10

Error Message

When attempting to upgrade Portal for ArcGIS from version 10.6.1 to 10.8.1, the upgrade process fails, returning the error message:

Error:   
There was an error when attempting to upgrade the existing portal. com.esri.arcgis.portal.admin.core.site.migration.MigrationException: Failed to upgrade the PostgreSQL from 9.6.8 to 10.10.
For more information, please view the log messages located in the content directory specified during setup (C:\arcgisportal\logs)

Attempting to upgrade Portal for ArcGIS from the Portal Administrator Directory returns the same error.

Cause

The Portal for ArcGIS PostgreSQL database administrator username used during the upgrade process does not match the username listed in the configuration files of Portal for ArcGIS.

Solution or Workaround

Before upgrading, update the Portal for ArcGIS PostgreSQL database administrator username to reflect the current Portal for ArcGIS administrator username.

1. Log in to the Portal Administrator Directory with an administrator account.
2. Navigate to Home > System > Database.
3. Click Update Admin Account.
4. Enter the current Portal for ArcGIS username and password in the required fields. Click Update Admin Account.

Successfully updating the administrator username allows the upgrade process to run successfully.