Attempt to send a notification fails with an exception:
No send methods specified for this type of notifications
All the sending methods are disabled.
If exception occurs only for the specific account - enable at least one method in the customers control panel: CCP > Account > Account Settings > How to notify me
If exception happens for all the customers - enable at least one method in the providers/resellers control panel:
Home > System > Settings > Notifications > Message Categories
The category depends on the notification attempted to be sent.