This Knowledgebase article provides information about why one should wait 10 minutes before performing a second switchover on a Neverfail server pair.
The time to establish domain authentication after a switchover or failover varies depending upon several environmental factors such as the load on the domain controller and the topology of the domain.
This is not normally an issue with a single switchover unless the network connectivity to the domain controller is slow or the domain controller is busy. However, if a switchover or failover is followed by another switchover within a 10-minute period, Microsoft System Attendant may fail to start because the secure channel has not been re-established before the System Attendant begins to start.
To ensure system stability and guarantee application start-up, Neverfail strongly recommend that a switchover is not performed within 10 minutes of a switchover or failover occurring.
To recover Exchange should it fail to start in this situation, open the Neverfail Management Client and proceed to the Application Manager. Simply start the Exchange Application. You are unlikely to encounter this problem when switching after a failover because of the time take to resynchronize the logs and databases.
If you continue to experience problems with System Attendant, after following the above advice, please contact your Neverfail Support Center.