Sergey,
If your requirement is to load data to BPC via web services, why not use BPC's web services as the endpoint? In 7.5, I wrote some jquery to load csv files from a Sharepoint document library via BPC's data manager web service.
If you want to use native BW data loading techniques (and you have implemented the technical name note), you can but there are several things you must do like switching the cube out of planning mode.
Hope this helps,
Jonathan