DragDrop application goes wrong when changing screen size

I am making a small application on android, it is based on dragdrop with shadowbuilder, i used an emulator with screen wvga800 (800x480), it was working fine, when draging an element to a grid it drops properly in the destination grid. Then i used another emulator with screen wxga800-7in (1280-800), it went all wrong, the elements dont drop anymore inside the grid, they appear to shift to another position. note: in the layout XML file the used unit is dp. What is excactly the problem here? please help.

Thanks in advance for any help.