Problem with ESXi 5 or Cisco servers (hosts disconnected)

Hi, since we change our servers for our ESXi 5 cluster, we have sometime host deconnection.

Servers specs is : 3x Cisco UCS C200 M2 (2x Xeon X5675 @ 3.06GHz and 96Gb memory)

Some times, without warnings, the host disconnect in vCenter.

We can still ping the host but cannot SSH or log with vSphere Client directly. If I want to log locally, as soon as I type the password and ENTER, it freeze and the only fix is hard restart. (and lost local logs)

While the host is disconnected, guests are disconnected but fully operationnal (remote desktop, ping). We can't vMotion or change settings on the guest since they are (disconnected)

Is anyone already saw that problem, it's really annoying.

Let me know if you need more informations.

Thanks and have a nice day,

Martin Bergeron