dbb4090d_Internal_Error_Codes___DocWiki__Descriptor
[Code] 23 [Explanation] A matched dial peer could not be used for the outbound leg because the gateway cannot translate between the inbound and outbound protocols. [Category] 47 [Descriptor] 
Incompatible protocols
Cisco IOS Voice Troubleshooting and Monitoring -- Cisco VoIP Internal Error Codes - DocWiki