How to create a calculation depending on a dimensional value (CASE)

[erwink]

I have a Dimension with Location -> Employee
I have a fact with Hours per Month per Employee

I have a Crosstab
                         
                                Year
                               -----------
Location | Employee| hours

My User request to have FTE Column displayed. FTE is 1/nbr_of_hours_inYear*hours
The nbr_of_hours_inYear is Location specific

I tried to create a DataItem with CASE [Location] WHEN [Loc1] THEN (1/1600*[PlanHours])...
Fired an error: The 'ces_when' function is not supported in the context in which it is used.
so I tried with IF THEN ELSE
Fired an error

See attachment
How can I do that?!