Exported date range pst only contains folder structure and no messages

hi all

I used the following powershell to try and extract a date ranged PST file for sent and received items between a specific date however when I open the extracted pst it only has the folder structure and no messages.

New-MailboxExportRequest -ContentFilter {(Received -lt '11/01/2008') -and (Received -gt '9/30/2009') -or (Sent -lt '11/01/2008') -and (Sent -gt '9/30/2009')} -Mailbox "john.smith" -Name JsmithExp -FilePath \\EX01\PST$\JS.pst

Any ideas where i am going wrong ?

thanks 

ollie