can't connect to esxi host via vsphere client

Hello,

I'm getting the error message below when i try to connect to esxi hosts.

"A communication error occurred while sending data to the server. (the underlying connection was closed: an unexpected error occurred on a send)"

I have two esxi hosts and i have this problem on both. I can ping them but i can't connect. There is no firewall between hosts and clients. After i restart the hosts, i can connect, but after a couple of days the problem occurres again.

Version informations are below:

ESXI 4.1.0 Build 348481

Vsphere client 4.1.0 Build 345043

Do you guys have any idea about this problem?

Thanks in advance.