Hi Tariq,
As already suggested by Raman, please migrate the data flows to 7.0 data staging technology. It is so easy to do it and offers so many advantages. Better spend you time on migration than on error solving the 3.x data flow.
Migration should be done for the whole data flow, all objects including the DataSource. BW release 7.4 offers convenient migration tooling. Please also refer to SAP Help.
Best regards,
Sander