Hi docwhit

Try the following in E21, copy across & down.

SUMIFS:
=SUMIFS($D$39:$D$50,$A$39:$A$50,">="&EOMONTH("01/"&$C21&"/2013",-1)+1,$A$39:$A$50,"<="&EOMONTH("01/"&$C21&"/2013",0),$C$39:$C$50,E$20)

Or a SUMPRODUCT:
=SUMPRODUCT(--(MONTH($A$39:$A$50)=$C21),--($C$39:$C$50=E$20),$D$39:$D$50)

Kevin