There seems to be an incorrect advanced option in VC U3.

HA network compliance check
During the configuration of HA in VirtualCenter 2.5 Update 2, the Task & Events tabs might display the following error message and recommendation:
HA agent on <esxhostname> in cluster <clustername> in <datacenter> has an error Incompatible HA Network:
Consider using the Advanced Cluster Settings das.allowNetwork to control network usage.
Starting with VirtualCenter 2.5 Update 2, HA has an enhanced network compliance check to increase cluster reliability. This enhanced network compliance check helps to ensure correct cluster-wide heartbeat network paths. VirtualCenter 2.5 Update 3 allows you to bypass this check to prevent HA configuration problems. To bypass the check, add das.bypassNetworkVerification=yes to the HA advanced settings.

The described option should actually be “das.bypassNetCompatCheck with the values  ”true” or “false. So keep this in mind!!!