SSRS 2008 R2 Subscription Email Error (only with Attachments)

I am having the same issue as in the following post http://social.msdn.microsoft.com/Forums/en/sqlreportingservices/thread/6a4ee2d8-23ce-4b68-a14e-fe7024cb58ea.

I have SSRS 2008 R2 set up on a Windows Server 2008 SP2 server.

Everything works fine, with the exception of subscriptions with an attachment.  If the subscription is just a link, it works fine.  In reviewing the log files, I get the following error info:

library!WindowsService_8!e6c!04/25/2011-13:32:06:: e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ServerConfigurationErrorException: AuthzInitializeContextFromSid: Win32 error: 5; possible reason - service account doesn't have rights to check domain user SIDs., Microsoft.ReportingServices.Diagnostics.Utilities.ServerConfigurationErrorException: The report server has encountered a configuration error. ;
library!WindowsService_8!e6c!04/25/2011-13:32:06:: i INFO: Initializing EnableExecutionLogging to 'True'  as specified in Server system properties.
emailextension!WindowsService_8!e6c!04/25/2011-13:32:06:: e ERROR: Error sending email. Microsoft.ReportingServices.Diagnostics.Utilities.RSException: The report server has encountered a configuration error.  ---> Microsoft.ReportingServices.Diagnostics.Utilities.ServerConfigurationErrorException: The report server has encountered a configuration error.
notification!WindowsService_8!e6c!04/25/2011-13:32:06:: e ERROR: Error occured processing subscription bf7ba260-6f39-4915-834c-70ca36a616ef: Failure sending mail: The report server has encountered a configuration error. Mail will not be resent.

When I review the KB article mentioned (link below), the top specifically says "NoteThis problem does not occur in Windows Server 2008"

http://support.microsoft.com/kb/842423

Since I have it installed on a Windows Server 2008 box, and am experiencing this issue, is there something different that people know of for that version of Windows Server?

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- Glenda