Your admin account owns the workbook, but your non-admin account is the one subscribed. VizAlerts won't allow any random subscriber to a workbook to fire off VizAlerts, when they're an "advanced alert". In this case, you will need to subscribe with your admin account, that's all--then it will work fine.
See this Issue on the possibility of allowing non-owners to execute a VizAlert.
Hi Jens. If this answered your question, would you mark my answer as correct, please?