SumIf won't work on part of spreadsheet

I'm having a problem which seems like it shouldn't happen. I have a weekly spreadsheet which reads a list of readings and dates. Then it sums up a total for each week. I added this weeks numbers to the data list and then added some new entries to look up the answers for last week (Week 11 of 2005). But it shows Zero even though there are some numbers in the data to add. The formula is just the same as the box above. In fact I dragged it down. It advances the numbers that should advance and does not advance the numbers that shouldn't. The formats of the data numbers and answers are all the same.
For this last week's entry it looks at the adject box where it reads 2005.11 (Year, week) but it says "0". So I changed it to 2004.11, and it works for the old data. It works right up to until last week and then zeros. I checked the range that it's searching the data for and it is all correct.
I don't see how it can work for 5 years and then stop working on just last week's data. Is there something I'm missing? Thanks.

Chuck.

Could you send an example?

Ola