You should have 2 web documents (not the ones that are in the browser) that are stated into web documents like(*html,*htm,*php,*asp, etc) . . .and your code was
<frameset rows="20%,80%"><frame src="frame_a.htm"><frame src="frame_b.htm"></frameset>
It should be . . .
<frameset rows="20%,80%"><frame src="*your own document*"><frame src="*your own document*"></frameset>