4f55f5cb_ISDN_Cause_Codes__Cause_Usage
[Cause#] 99 [Fixit!] N/A [Cause Summary] Information element non-existent or not imlememted. [Cause Usage] 
Indicates that the equipment sending this cause has received a message that includes information elements not recognized because the information element identifier is not defined or it is defined but not implemented by the equipment sending the cause. However, the information element is not required to be present in the message in order for the equipment sending the cause to process the message.
ISDN Cause Codes
Cause Usage