4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 96 [Enumeration] MANDATORY_IE_MISSING [Cause] mandatory information element is missing [Q.850] [Description] 
This cause indicates that the equipment sending this cause has received a message which is missing an information element which must be present in the message before that message can be processed.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description