Exchange is responsible for the publication of Free/Busy information when applications use CDO (such as ERM) for processing meeting requests. ERM does not physically push out Free/busy information as Outlook does. Rather it relies on Exchange to poll for updates to Free/Busy information. Please reference the following link for a detailed description of this process: http://msexchangeteam.com/archive/2004/08/19/217187.aspx.
There are registry entries that can be made on the Exchange/ERM server that will affect how many months and how frequently Free/Busy information can be updated. Refer to the following website for additional information: http://www.swinc.com/products/ERM/troubleshoot.asp?status=viewquestions&categoryid=6