%windir%\Sysnative\cmd.exe /c PowerShell.exe -PSConsoleFile "C:\Program Files\Microsoft\Exchange Server\bin\exshell.psc1" "C:\Mailbox.ps1"
Worked for me too - thanks!!!!
I am using this command to check Exchange mailbox sizes:
Get-MailboxStatistics | Sort-Object TotalItemSize -Descending | ft DisplayName,@{label="TotalItemSize(MB)";expression={$_.TotalItemSize.Value.ToMB()}},ItemCount