Nested grid problem

I got this error when add nested grid,

Fatal error: Class ‘grid_detail_transaction_sub_css’ not found in C:\Program Files (x86)\NetMake\v81\wwwroot\scriptcase\app\mleaf_admin\grid_transaction\grid_transaction_grid.class.php on line 1419

I follow from sample, http://www.scriptcase.net/samples/tutoriais/grid/grid25.php

Anyone have some idea?

TIA

Daniel