Find The Median Call Length For Calls In A Certain Month

I've read several threads about using Median(If, and I have success with one criteria, but not with three. Here's the setup:

I have a log of phone calls, and I want to find the median call length for calls in a certain month or set of months (i.e. a quarter, three months). In Calls!B I have the date of the call, in Calls!C I have the call length in minutes (i.e. "34"), and in Calls!A I'm using Concatenate and Text to return month/year (i.e. "Aug06").

With one criteria, it calculates the median correctly. With three, it only returns #NUM. Yes, I hold control+shift and hit enter. Here's my formula:


=MEDIAN(IF(Calls!$A$2:$A$500=Scores!B8,IF(Calls!$A$2:$A$500=Scores!C8,IF(Calls!$A$2:$A$500=Scores!D8,Calls!$C$2:$C$500)))))
Where Scores!B8,C8,D8 hold "Oct06" "Nov06" and "Dec06" respectively. What am I doing wrong? Is there another approach I should use instead?