Using s40 Theme Studio 2.2, creating themes for Nokia 7373 (firmware 3.81)

I have created 240x320px image as background (main) and added it to my theme in Default > Background(main). The images appear OK in the Studio, but when the theme is uploaded to my phone, it doesn't appear - the background(grid view) images appear instead of it!

Before i used s40 theme studio 2.1, for my old nokia 7370, and i never had this problem!

Has anyone been able to change it successfully, or can't it be done?