When Networking Configuration Operation Is Rolled Back and a Host Is Disconnected from vCenter Server?

In vSphere 5.1 or later, an attempt to perform a networking configuration operation on a vSphere Distributed Switch on a host, such as creating a virtual machine adapter or a port group, causes the host to disconnect from vCenter Server and results in the error message Transaction has rolled back on the host.

Reason
Under stressful conditions on a host, that is, if many concurrent networking operations compete for limited resources, the time to perform some of the operations might exceed the default timeout for rollback of network configuration operations on the distributed switch. As a result, these operations are rolled back.

For example, such a condition might come up when you create a VMkernel adapter on a host that has a very high number of switch ports or virtual adapters, all of which consume system resources on the host.

The default timeout to roll an operation back is 30 seconds.

To Change this Timeout 
1. Select vCenter Server in Inventory
2. Click on Manage Tab
3. Settings > Advanced Settings
4. Find out this Property ---- config.vpxd.network.rollbackTimeout 
If present Modify the Value. If not present create it and enter the value. Value will be in Seconds. > Click OK
5. Restart vCenter Server