[strongSwan] strange problem with migrate a ikev1 psk from openswan to strongswan

[Falk Hackenberger]

Hello,

I have a very strange problem with a migration a ikev1 psk vpn from 
openswan to strongswan
The old system have a Debian kernel 3.2.46-1+deb7u1~bpo60+1 with openswan
2.6.28+dfsg-5+squeeze2.
Then new system is have a debian kernel 3.16.7-ckt7-1 (2015-03-01) with
strongswan 5.2.1-5.

On the old system the vpn connection have no problems.
On the new system the ike exchange have no problem.
But I get no answer to the esp packets.
I knew that the esp packets arrive the other side which is a checkpoint.

As the checkpoint is controlled by customer I cant debug there.
Any Idea what is the reason for that problem?

Thanks Falk