I could only resolve it with restarting the host. There was another problem too. I have found out after restarting the Vcenter which is a VM on the host in question that suddenly the host and all its associated VMs were disconnected in the Vcenter. Strange was that I couldn't ping the host from the Vcenter server, but I was able to ping the host from other machines on the network.
A host reboot resolved it. I'm not sure, but I think that it is not the first time where I suddenly couldn't ping a ESXi host within Vcenter. We are using ESXi 5.5.
Thanks,
Edy