Cannot complete VPN phase 1: NO_PROPOSAL_CHOSEN

Greetings,

Let me preface this by saying that I have checked the documentation for the recommended phase1 configuration and I still cannot complete phase1. My device is an ASA 5520 running 8.4,

Upon sending traffic I receive log messages:

2014-06-02T23:45:14.343085-05:00 hostname.redacted : Jun 02 23:45:14 CDT: %ASA-vpn-5-713904: IP = azure_gateway.redacted, Received an un-encrypted NO_PROPOSAL_CHOSEN notify message, dropping
2014-06-02T23:45:14.343085-05:00 hostname.redacted : Jun 02 23:45:14 CDT: %ASA-vpn-4-713903: IP = azure_gateway.redacted, Information Exchange processing failed

Isakmp SA:

 6   IKE Peer: azure_gateway.redacted
    Type    : user            Role    : initiator
    Rekey   : no              State   : MM_WAIT_MSG2

Relevant config:

crypto ipsec ikev1 transform-set L2L_AZURE esp-aes-256 esp-sha-hmac

crypto map OUTSIDE_VPN 80 match address L2L_AZURE
crypto map OUTSIDE_VPN 80 set peer azure_gateway.redacted
crypto map OUTSIDE_VPN 80 set ikev1 transform-set L2L_AZURE
crypto map OUTSIDE_VPN 80 set security-association lifetime seconds 3600
crypto map OUTSIDE_VPN 80 set security-association lifetime kilobytes 102400000

crypto ikev1 policy 20
 authentication pre-share
 encryption aes-256
 hash sha
 group 2
 lifetime 28800

tunnel-group azure_gateway.redacted type ipsec-l2l
tunnel-group azure_gateway.redacted ipsec-attributes
 ikev1 pre-shared-key key.redacted

I have other ikev1 policies but the one listed should meet the requirements listed here.

Is there something I am missing?

Thanks in advance.