I currently have a grouped dataset with a number of columns. One of these columns named "Cumulative Total Usage" has the below formula on it;

 'IF (  ISERROR([Cumulative Total Usage(-1)]),  [R: Sum Total Qty(+1)],   if(ISERROR([Cumulative Total Usage(-1)]),1,0) )'

When I try to render the grid, it spits out an error "Column had an error in the forumla - IF (  ISERROR([Cumulative Total Usage(-1)]),  [R: Sum Total Qty(+1)],   if(ISERROR([Cumulative Total Usage(-1)]),1,0) ) - with the error - Invalid or unavailable reference."

 I have followed the examples of running totals, and this appears to work fine - can anyone explain why this would not work?