I can't tell you why the snippet won't work in your particular application since we don't have the time and resources to provide end-to-end consulting support (not without a Statement of Work anyway) and learn the context within the application, which may hold all the secrets to why this works or not.
However, I would propose...
a) Take out the filtering on O#Top. It's not doing anything because you're going to include all Origin members from the source anyway. If you want to aggregate to a single target Origin member then set this on the ExpressionDestinationInfo and then use the aggregate option in the SetCell in the loop. ( SetCell(si, cell, Aggregate=True)
b) Have you done a LogDataBuffer, immediately after opening the source buffer? Does it output any intersections?
c) Does the destDatabuffer contain any cells , just before the SetDataBuffer?
d) I would pay particular attention to any fixed common members in the source databuffer which may get substituted for the special member XFCommon. Also ensure the ExpressionDestinationInfo is referrred to when opening the source buffer (as an optional argument).
