Scenario: I've created a form with multiple data sources, one of the tab pages needs its own new, delete button. (Can not use design property). When adding command buttons for New and delete, New works fine but delete doesn't.
Possible reason: There is a lot of commands which start with Delete, and probably you have chosen the 'Delete' command, while you need to choose 'Delete record' as this button spouse to delete a record (or multiple records). Try this.