Deferment happens anytime an account using the Salesforce Marketing Cloud Connector isn't able to authenticate or contact Salesforce Core when attempting to push tracking back.
When Exacttarget is integrated with Salesforce we create a tracking user. If the tracking user password is changed in the Salesforce we receive Deferment Notice email from exacttarget. The new salesforce password needs to be updated in the exacttarget for that tracking user.
Exacttarget: Admin > Account Settings > Tracking Configuration > Salesforce Integration > Edit
Tracking User Password (Enter the new password)