Get Exchange folder size using Redemption.dll fails when used from Outlook2007

Question

I am using Redemption.dll (Version 4.7.0.1026- latest) in an Outook (2003/2007) Add-in where i need to retrieve the exchange mail box size. To get the folder size, I am using the function get_Fields():

foreach (RDOStore store in rdoSession.Stores)
{
  int size = 0;
  if (store.StoreKind == TxStoreKind.skPrimaryExchangeMailbox)
  {
    // ****
    size = (int)store.get_Fields("http://schemas.microsoft.com/mapi/proptag/0x0E080003");
    mailBoxSize += size;
  }
}

This function returns folder size when called from Outlook 2003 Add-In, but if I call the same from Outlook 2007 Add-In, it returns null object. Does the Redemption.dll not support outlook 2007 completely or is it a different API call? Please let me know if any one has some info about it.