=SUMIFS(Detail!C:C,Detail!A:A,"=B6",Detail!A:A,"< =C6",Detail!B:B,"Installation")

Detail Sheet
Date Type Qty
2/8/2010 Sales 2.00
2/8/2010 Credits 1.00
2/10/2010 Sales 1.00
2/12/2010 Credits 3.50
2/12/2010 Sales 1.00

I am trying to summarize
Week No. Start End Sales
1 2/1/2010 2/5/2010 0
2 2/8/2010 2/12/2010 0
3 2/15/2010 2/19/2010 0

But this seems to be ignoring my date test. Is there something I am
missing? (Note - when I test for other types of things (not dates as a test)
it works)