Index Indirect Match problem

I come to you for help once again.

I'm probably being thick, but I can't get the following formula to work:

=INDEX(INDIRECT($A$6),MATCH($A$7,$A$21:$A$24,0),MATCH(B$6,$B$20:$M$20,0))

I've placed it in a work book to retrieve annual data based on selections from combo boxes but I can't get it to work!

I include the worksheet to show you what I'd like.

Help!

Steve