Hi Chris,
I thought that this may be what you were looking for;
Determining the Cause of Failover or Failback from an Event ID
This section describes how to determine the cause of failover and failback based on the event IDs that appear in the Event log.
To Determine the Cause of Failover or Failback from an Event ID
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Step 1 On the primary server, on the Windows Start menu, click Programs > Administrative Tools > Event Viewer.
Step 2 In the Tree pane on the left, click Application Log. The log appears in the right pane.
Step 3 Locate the entries that show CiscoUnity_NodeMgr in the Source column.
Step 4 For the entries, note the event IDs that appear in the Event column.
Step 5 On the secondary server, repeat Step 1 through Step 4.
Step 6 Use Table 3-2, which follows the procedure, to determine the cause of failover or failback.
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/failover/guide/dom/5xcufgd030.html#wp1131566
Hope this helps and best of luck!
Rob