It looks like you should create another calculated measure on the cube, which would go one level up (.parent) and calculate the currentmember against its parent.
What are the facts on the cube?
What soes the Task Completed % calculated measure do (code)?
M.Sc.IT, M.B.A, MCTS BI 2008, MCITP BI 2008, MCTS SQL Dev, CSM, CDVDM