Move-SPUser trouble

Hi @all,

I try to change some usermapping in my SharePoint Foundation Farm with the following command in the powershell:

move-spuser -IgnoreSID -Identity ADD\M45443 -NewAlias ADI\M45443
OR
move-spuser -IgnoreSID -Identity "ADD\M45443" -NewAlias "ADI\M45443"

Unfortunately I get this errormessage:

Move-SPUser : The parameterless Read method can only be used when this instance was initialized with an SPUser object.
At line:1 char:12
+ Move-SPUser <<<<  -Identity "ADD\M45443" -NewAlias "ADI\M45443"
    + CategoryInfo          : InvalidData: (Microsoft.Share...PCmdletMoveUser:
   SPCmdletMoveUser) [Move-SPUser], InvalidOperationException
    + FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SPCmdletMoveUser

Do you have any idea what's wrong with my command?

Thanks in advance

Ozzl