Assignment Notification allows a user to receive an Email when someone else has scheduled a new Task on their behalf. One way in which AdvoLogix adopts task notification into our workflow is via Action Plans. Activities within an Action Plan optionally have the ability to send an assignment notification on a task by task basis.

Salesforce.com Winter 15 Changes
The behavior of Task Assignment Notification changed with the Winter 15 platform release. In short, a new global option was added which allows individual users the ability to disable their Assignment Notification on a user by user basis. This option is enabled by default.

AdvoLogix 1.44.3 Behavior
When the new global option is enabled, new behavior currently prevents AdvoLogix Action Plans from sending email notifications. Impacted are those organizations using the Email notification option from an AdvoLogix Action Plan item.

When enabled the new global option prohibits an AdvoLogix Action Plan from sending Email notifications, regardless of the setting on the Action Plan.

To check your setting go to:   Setup  |  Customize  |  Activities  |  Activity Settings

UserTaskAssign

Enable User Control over Task Assignment Notifications

For action plan task assignment notifications to be sent this option will need to be unchecked.