IKE error between two 3000 concentrator. "unencrypted packet"

[verusadmin]

I am trying to connect two sites with VPN 3000 concentrators and IPSec tunnel. I've done this several times with other clients sucessfully but not this time. I get this strange IKE error in phase 1.

"received an unencrypted packet when crypto active!! Dropping packet."

I checked the connect settings and we are all using same encryption type and all. Where should I start loolking? What are the possible cause of such error?

Thanks.

dj

[verusadmin]

Problem solved. It was mismatched pre-shared key!!!

[lexibrian]

This is a good answer.

I spent quite a while debugging a connection between a 3005 concentrator and a Checkpoint firewall at a remote site. All the settings looked fine, but phase 1 kept failing and I noticed the above error.

Suggested to remote admin that we change the PSK and the tunnel came up right away.