Mailbox export request always failed

HI

I would like to export mail to pst file using command below:

New-MailboxExportRequest -Mailbox vik.kuc -FilePath \\mbx01\d$\vk\vk.pst  -ContentFilter { (Sent -lt '09/20/2013') -and (Sent -gt '09/15/2013') }

Always get status request failed  and file vk.pst was created with size 271360

How to resolve it?

Thanks in advance