IAX2 routing out SIP

I have a system that only connects via IAX2. I need to setup an asterisk server to sit between this application and the forwarding provider. I need my application to connect to Asterisk over IAX2 and the Asterisk server to connect to the vendor over SIP. From what I can tell Asterisk appears to be connecting to the provider properly. I am seeing TX Frame Retry errors when I try to connect the application.

Tx-Frame Retry[001] – OSeqno: 001 ISeqno: 001 Type: IAX Subclass: LAGRQ
Timestamp: 10013ms SCall: 05772 DCall: 00001 192.168.5.21:49759
Tx-Frame Retry[000] – OSeqno: 002 ISeqno: 001 Type: IAX Subclass: LAGRQ
Timestamp: 20013ms SCall: 05772 DCall: 00001 192.168.5.21:49759
Tx-Frame Retry[000] – OSeqno: 003 ISeqno: 001 Type: IAX Subclass: PING
Timestamp: 21013ms SCall: 05772 DCall: 00001 192.168.5.21:49759
Tx-Frame Retry[001] – OSeqno: 002 ISeqno: 001 Type: IAX Subclass: LAGRQ
Timestamp: 20013ms SCall: 05772 DCall: 00001 192.168.5.21:49759
Tx-Frame Retry[003] – OSeqno: 000 ISeqno: 001 Type: IAX Subclass: REGAUTH
Timestamp: 00013ms SCall: 05772 DCall: 00001 192.168.5.21:49759
AUTHMETHODS : 2
CHALLENGE : \x31\x37\x33\x38\x35\x35\x32\x34\x34
USERNAME : MyUser

Is there something that I am missing? My iax.conf file has this:

[MyUser]
type=user
username=MyUser
secret=MyUser
host=dynamic
context=default
requirecalltoken=no

Have you done any packet captures to see if the traffic is getting lost?