>I have report with a4 page setup defined.I need jpg picture exactly 21*29.7cm (a4 format) in detail band. Problem is error "detail band is too large". Any solutions?

Each printer has none-printable area on all sides of the page. As result, the report can only occupy that area. You may set Printable Area in the Page Setup too the whole page which will result in the report areas not printed outside of the print area.