Errors running the Export-PublicFolderStatistics.ps1

I am currently trying to migrate my exchange 2007 public folders to my exchange 2013 cu14.  when running through the migration steps I'm getting errors with the Export-PublicFoldersStatistics.ps1.

You cannot call a method on a null-valued expression.
At C:\Windows\system32\Export-PublicFolderStatistics.ps1:193 char:88
+ $ipmSubtreeFolderList | %{ $script:IdToNameMap.Add($_.EntryId, $_.MapiIdentit
y.ToString <<<< ()) };
    + CategoryInfo          : InvalidOperation: (ToString:String) [], RuntimeE
   xception
    + FullyQualifiedErrorId : InvokeMethodOnNull

This is what my CSV file looks like.

I have ran this with the appropriate permissions and am still getting the same error.

Any info would be greatly appreciated

Thanks

Loughness