The control account set field is six characters long, but your specific code uses only 3 characters. I believe you will have to use 3 leading spaces in your formula to get it to be recognized properly. For example:

if Control Account Set = " USA" then cost*qty shipped/1.5 etc etc.

If this doesn't help (though I think it will), then put each of the fields you are using in the formula into the detail secion of the report, and manual judge from a print preview what the formula is doing wrong.

Regards,
Softrak Support