What would cause this error on a WS running ZCM

Device Alias: XYZWS
Device IP Address:
Warning: [7/12/16 1:38:08 PM] RefreshMgr ZMD.RefreshHandlerException Unexpected exception received when refreshing handler
ActionManagerRefreshHandler(ITEM_REFRESH): Key cannot be null.
Parameter name: key

1. How do I know what bundle this refers to or if it refers to the agent itself?

2. What 'handler' is it referring to?

3. What does 'Parameter name: key' mean??