Free Busy not working from Exchange to Notes.
When looking in the DominoFreeBusyService.exe.log file the following error is seen:
2012-05-29 10:53:33,709  ERROR DominoLibrary - GetFreeBusyInfoFromDateTimeRange()
QuestSoftware.CMN.API.FreeBusy.DominoLibrary2.DominoErrorException: This database is currently in use by another person or process, and cannot be accessed at this time. In order to share a Notes database, it must be accessed via a Domino Server by all users of the database.
at QuestSoftware.CMN.API.FreeBusy.DominoLibrary2.DominoLibrary.GetFreeBusyInfoFromDateTimeRange(List`1 i_emailAddresses, List`1 i_userNames, Void* pUserList, DateTime i_startTime, DateTime i_endTime, Boolean i_isGroup)
This can be caused due to the Notes Client on the Coexistence Manager for Notes (CMN) server where the Domino Free/Busy Connector is installed being open.
Close the Notes client and restart the Quest Coexistence Manager for Notes Domino Free/Busy Connector, then attempt the Free Busy lookup to verify it is now working.