Named set issue

Hello

Can anyone please tell me how to fix the error: "Error occurred retrieving named sets: MdxScripts(Sales) (8, 5) The 'Account Number' hierarchy appears more than once in the tuple." in mynamed set below?

The MDX scripts after it works fine!

CREATE DYNAMIC SET CURRENTCUBE.[Sample Accounts]
 AS (
[Account].[Account Number].&[7158828],
[Account].[Account Number].&[7158828],
[Account].[Account Number].&[7158828],
[Account].[Account Number].&[7158828],
[Account].[Account Number].&[7158828],
[Account].[Account Number].&[8083198],
[Account].[Account Number].&[8083198],
[Account].[Account Number].&[8083198]
)

MDX script (works):

select
{
	[Account].[Account Number].&[8083198]
,	[Account].[Account Number].&[7158828]
,	[Account].[Account Number].&[8083198]
} on columns
from
[Sales]

Amir