This message indicates that the password of the mail server is not correctly configured. You can check the following in your Scheduler Administration Tool,
In the Scheduler Administration tool navigate to Configuration > Server Configuration > Mail Configuration panel and press "Edit mail configuration" button. Here ensure that you have the fields "username" and "password" are being stored with the corresponding values.
Finally you can click on the “Test mail configuration” button to validate if you are able to send email configured using Denodo Scheduler.
For more information I would ask you to refer to the section [Mail Configuration](https://community.denodo.com/docs/html/browse/6.0/scheduler/administration/administration/server_configuration/server_configuration_sections) from Scheduler Administration Guide.
Hope this helps you!