Calculated Member only gives out null Values, Why ?

I Need to do the following calculation in mdx (i hope the code is straightforward, if clarification is needed please tell)[b]([Orders].[Customer].CurrentMember, [Measures].[InvoiceAmount]) / (Root([Orders]), [Measures].[InvoiceAmount])[/b]but all I'm getting is NULL Values, can anybody see what is Wrong ? Thanks to all of you in advance, your always great help is much appreciated.SQL Server 2012