"Drush cannot find your database connection details"
Drush no longer allows you to define a 'database' record in your site alias file for use with sql-sync.  This used to work in earlier versions, but is no longer supported.  Make sure that the source and target sites both have valid settings.php files that include the database information.

To test:

drush @hpc.dev sql-conf


If your database connection is correct, it will be displayed. Using sql-conf on each site can help isolate which one is having a problem with its connection info.