I have A1:A4 cells filled with -1,2,3,4 and named the range A1:A4 "sales"

in A6 I have =SUM(IF(sales0,sales)) outcome 8 (=-1+2+3+4) and it should be
2+3+4=9

When I click the Fx button to edit the formula, the outcome is correctly
shown as 9 ?

Can anybody tell me what I am doing wrong here?

I am using excel 2003 SP2