I don't know about the Aria systems, but the Lucent systems, Sierra and IMA-CA have an option to turn this error off. Also, you can turn off outcalling in menu 9.
This happens when users login, then press 4, for notification, then 1 to turn it on. Thinking it is for
MWI. The user interface allows this to happen without a schedule or number.
You are right, turning it off in the COS does not stop it. Outcalling needs to be set to no in the COS initially, and allowwed only for those who need it.