Cascading combo boxes in Datasheet view

[cliffschooling]

I want to create a Form called "Timesheet" with a subform "Downtime" linking to a table. The data is to be entererd through a datasheet view with 3 cascading combo boxes linked to 3 tables DTmain, DTsub and DTsubsub. I can get the tables to refresh to the relevent data in a form, but cannot get them to work in a subform. I know the problem lies with the reference to the form & field names, but cant seem to get it right