Ok, but blanks still evaluate to 0. Do you mean they're not actually blank, as in empty string "" or space " " or what?
As you can see, it's not failing as you have described the problem:
Excel 2010
<colgroup><col style="width: 25pxpx"><col><col><col><col><col><col><col><col></colgroup><thead>
</thead><tbody>
[TD="align: center"]1[/TD]
[TD="align: right"][/TD]
[TD="align: right"]4[/TD]
[TD="align: right"][/TD]
[TD="align: right"]5[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[TD="align: right"]20[/TD]
[TD="align: center"]2[/TD]
[TD="align: right"][/TD]
[TD="align: right"]5[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
</tbody>
Sheet1
[TABLE="width: 85%"]
<tbody>[TR]
[TD]
Worksheet Formulas[TABLE="width: 100%"]
<thead>[TR="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=DAE7F5]#DAE7F5[/URL] "]
[TH="width: 10px"]Cell[/TH]
[TH="align: left"]Formula[/TH]
[/TR]
</thead><tbody>[TR]
[TH="width: 10px, bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=DAE7F5]#DAE7F5[/URL] "]H1[/TH]
[TD="align: left"]=SUMPRODUCT(
($C:$C="Equity")*($E:$E)*($B:$B))[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
</tbody>[/TABLE]