Failed to start the selected triggered send(s): A problem occurred Starting the following Triggered Sends. Please contact Customer Service for additional information.Name : NewTestDemo\ External Key : NewTestDemo \ Message :\ The email ID=355, contained 4 validation errors. Refer to the Triggered Send Email Validation error log, ID = 790560228
You should run the toolbar Validate from Content -> Emails -> (your email). This is most likely caused by missing required personalization strings -- like the physical mailing address, profile/preference center links, the unsubscribe link, etc.