Configure managed accounts - object reference not set to an instance of an object

Run the following powershell command to display all Managed Accounts 

Get-SPManagedAccount | Select Username, Automaticchange

Find out the account which has automatic change value as True, set it false

$managedact = Get-SPManagedAccount -Identity "dom\Account from the above command"

$managedact.AutomaticChange=$false

$managedact.Update()

You can access the managed accounts from CA