ohjoo kwon

What measure do you want to sum?

If you define a calculated member on the measures dimension and omit the
measure to sum,
the calculated member will try to sum the calculated member itself,
SumOfTop10pctInternetSalesOrder,
which causes infinite recursive computing.

Modify the formula as following;

sum(
toppercent([Internet Sales Order Details].[Internet Sales
Orders].[Order Line].Members, 10, [Measures].[Internet Sales Amount]),
[Measures].[Internet Sales Amount]
)

Also, I recommend you define named set for 'toppercent([Internet Sales Order
Details].[Internet Sales Orders].[Order Line].Members, 10,
[Measures].[Internet Sales Amount])' and reuse it.

Ohjoo