Iif MDX Strings

Hi

Have the following Code

Iif([Practices].currentmember.level.name="All Practices",
string1 espression,
StrToValue([Practices].currentmember.Properties("Normalised"))

Currently when I browse the data for the All Practices Level I get #ERR.
For the levels below (known as PCT) I get values.

What do I need to enter into the string1 esporessiom part so that it gives me the sum of the 2nd level.

ie: If level 1 = All Practices, give me the total of ther normalised values from the PCT level, else give me the normalised value as is....ie:

If PCT1's normalised value = '1000'
and PCT2's normalised value = '2500'

Then I want the All Practices level to show 3500 and not #Err