vSphere HA detected that this host is in a different network than the master to which vCenter Server is connected

Hi all

I try to install a vSphere 5.1 environment (vCenter 5.1 (799731)).. it was never that hard to get a VMware product running.

Problem: 

As soon as i create a HA Cluster (with 2 ESXi 5.1 (799733)) i receive the message:

     "vSphere HA detected that this host is in a different network than the master to which vCenter Server is connected"

I have tried everything..

     place vCenter in other Networks

     Multihome vCenter

     place vCenter in the same network like the ESX hosts

     doublechecking ip's, subnets, gw's, name resolution, vSwitches

nothing helps.. is it a bug?

vCenter and also the two ESXi Hosts resides now in the same L2 network.

ESX1:     10.254.250.74     255.255.255.0

ESX2:     10.254.250.77     255.255.255.0

VC:          10.254.250.29     255.255.255.0

The message can't be correct.

Please.. @ anybody out there... HELP! I'm at the end of my knowledge.

Regards

Adrian