4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 97 [Enumeration] MESSAGE_TYPE_NONEXIST [Cause] message type non-existent or not implemented [Q.850] [Description] 
This cause indicates that the equipment sending this cause has received a message with a message type it does not recognize either because this is a message not defined of defined but not implemented by the equipment sending this cause.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description