need troubleshooting tip for vpn connections

[badguy]

I need help troubleshooting VPN connection. I get the following error messages and I want to know things to check out for when these errors occur.

attribute_unacceptable: ENCRYPTION_ALGORITHM: got AES_CBC, expected 3DES_CBC
message_negotiate_sa: no compatible proposal found
dropped message from 1.2.3.4 port 500 due to notification type NO_PROPOSAL_CHOSEN

I believe this has to do with mis matching parameters in the negotiation stage but I am 100% sure I have same parameters as I have copied and pasted all the files I used and not edited manually. Is there any other reason I will get this error? What are things I can do to correct it or what should I check out for?

transport_send_messages: giving up on exchange peer-1.2.3.4, no response from peer 1.2.3.4:500

I have no idea why this comes up.


Should I be able to ping the peer IPs from the VPN machine?
Should I be able to ping the peer IPs from the gateway machine?
Any troubleshooting tips will be appreciated.

Thanks