Are you sure there are no other errors in the windows event logs? Have you tried turning up diagnostic logging on the Exchange server to see if we can capture more items? Does this only happen on reboot? Cold boot or warm boot? Is it just the Informaton Store that won't start or are there other Exchange services that won't start? I wonder if there is a delay in one of the dependent services which then causes the Info store to not start. Do you have alerting set up to monitor the Info Store service and attempt a restart if the service is stopped?