having personal edition so cannot open qvw but I think Event values in set expression needs to be in single quote, It appears 'I' and 'O' are text values so may need single quote. Not sure if more things involved.
In the attachted fiel you can see the table with the expressions IN and OUT. About this 2 expressions you want to make a accumulation. The Goal is to have a table or a diagramm with dimension Month_Year and a accumulation about the several lands... Rigth beside the table you can see the right result !