First thing to do is to see exactly what value $(vG.LastWeek) holds by placing a text box onto your page and adding =$(vG.LastWeek) remember the equals sign before it Based on that result - assuming it returns a single value like 24 then you should be able to use your code without double quotes and double dollar notation because numeric values do NOT require quotes ie. (Sum({$<YearWeek={$(vG.LastWeek)}>}($(vExp.OQ))-($(vExp.DQ))))
e.g. if $(vG.LastWeek) returns a string like "week24" then you need single quotes (Sum({$<YearWeek={'$(vG.LastWeek)'}>}($(vExp.OQ))-($(vExp.DQ))))
i.e. if you want to select where less than or equal to the max week (assuming it returned a number like 24) then you need the double quotes to change the set analysis into a "search" (Sum({$<YearWeek={"<=$(vG.LastWeek)"}>}($(vExp.OQ))-($(vExp.DQ))))
Lastly check other of the other two variable are in fact returning the values you are expecting them too. (same way with a text box)
