Esxi 5.0 SSH will not stay started

Hello,

I have a problem on a Esxi 5.0 U1

I start the ssh service (the ssh port is open for all).

After a few minutes (3 at 5 minutes)  the ssh service is down.

I have upgrade to Esxi 5.1 version but it's the same problem.

When I restart the Esxi the ssh is not started (i have set restart automatically before).

I can log on the Esxi with Vsphere

Thanks for help's