Symptoms
After changing the SQL server to point to another alias by running the K2 configuration management and change only the name to point to a different SQL alias that was actually pointing to the same SQL server. All work fine but when running K2 SmartForms with workflows the submission notification email is sent, but the approval notification email is not sent.
The Notification were working before I did that change.
I have look into the workflow process exceptions but I can no see any errors.
Diagnoses
Looks like changing the SQL server alias corrupted the Exchange Service account password.
Resolution
Renter the password for that account.