Customers are currently seeing issues where SBS 2008 servers receives faxes successfully, but intermittently faxes routed to email may fail. You may also notice that the Fax Server Services crashes (fxssvc) due to a CDO call. If you look within Fax and Scan Console the Incoming queue folder may show that faxes are in a retry or failed state. In normal troubleshooting you would enable protocol logging for the "Windows SBS Fax SharePoint Receive Connector" within Exchange Management Console and wait for the failure to occur. However, this time logging shows nothing. The reason for this is that the faxes are failing before the connection to Exchange 2007 so nothing is logged.
Full Article: SBS blog