Powershell Help - Exporting list of mailboxes to PST

Hi Everyone,

I'm trying to export around 30 old mailboxes to PST prior to removing them from the system completely. The script I've come up with seems ok, but I'm getting an error when executing:

The script:

Import-Csv c:\list.csv | %{New-MailboxExportRequest -Mailbox $_.UserName -FilePath "\\SERVER\Share\PST Backups\$_UserName.pst"}

The error:

The server or share name specified in the path may be invalid, or the file could be locked.+ CategoryInfo          : NotSpecified: (:) [New-MailboxExportRequest], RemotePermanentException+ FullyQualifiedErrorId : [Server=SERVER,RequestId=54f75210-2ab7-4a27-84ce-48cf1895709c,TimeStamp=26/05/2015 1:18
   :28 AM] [FailureCategory=Cmdlet-RemotePermanentException] 76CC515D,Microsoft.Exchange.Management.RecipientTasks.Ne
  wMailboxExportRequest+ PSComputerName        : server.domain.local

Perhaps there's an issue with my command, or maybe there's just something I'm missing altogether... any feedback is greatly appreciated!

Cheers,
Anthony