Ouch! I thought so…
This has always been a problem when using SAP BW as data source. This has something to do with SAP BW - BOBJ communication. Normally, the webi service restarts itself when it reaches it’s memory limit, but when using SAP BW it’s doesn’t function well.
I haven’t found or heard of a “solution” for this problem. Even upgrading to SP3 is not an assurance that this will be resolved. You can try looking at FP 3.3 documentation and see if this is resolved.
You can also try looking at these:
http://forums.sdn.sap.com/thread.jspa?threadID=1217627
https://bobj-board.org/t/158544/12
https://bobj-board.org/t/129937/3
https://bobj-board.org/t/122071
R.A. 
(BOB member since 2008-10-28)