This code works:

CREATE MEMBER CURRENTCUBE.[Measures].[Percent]
 AS 
    [Measures].[Sum]
    /
    ([Companies].[CompList].CurrentMember.Parent
        , [Measures].[Sum]),

But this one doesn't work (why? I cannot to realize... ):

CREATE MEMBER CURRENTCUBE.[Measures].[Percent]
 AS 
    [Measures].[Sum]
    /
    (strtomember('[Companies].[CompList]').CurrentMember.Parent
        , [Measures].[Sum]),

It's not working because that is not a valid member reference.

Member references should be a 3 part name in the form of either:

  [<Dimension>].[<Hierarchy/Attribute>].[<MemberName>]

or

  [<Dimension>].[<Hierarchy/Attribute>].&[<MemberKey>]

The string you are using is ambiguous and the server will not know how to resolve it.

However this code is not working too:

CREATE MEMBER CURRENTCUBE.[Measures].[Percent]
 AS 
    [Measures].[Sum]
    /
    (strtomember('[Companies].[CompList].CurrentMember').Parent
        , [Measures].[Sum]),



CREATE MEMBER CURRENTCUBE.[Measures].[Percent]
 AS 
    [Measures].[Sum]
    /
    (strtomember('[Companies].[CompList].CurrentMember.Parent')
        , [Measures].[Sum]),

I'm just trying to calculate percent by rows regardless of the data in those rows. Is there a correct way to do this?