Does SUMIFS have issues with merged cells or across multiple sheets??

I have an excel file keeping track of department expenses for the year. I have a sheet for each month that lists the money spent in each budget category and with vendor info and PO numbers. I decided to add another sheet that tracks my expenses year to date by summing according to vendor and budget category requirements but I keep getting a #VALUE error and I don't know why.... The only thing I can think of is that it doesn't like my merged cells or different sheets? I attached a file with a portion of the file I'm working with and would love some help/explanation/solutions. Thanks!!

For example (if you open the file), I'd like to add all POs that are in the Cleaning Supplies category from the vendor Economical Janitorial. And do that across all 12 months/sheets to get a yearly total.

Please give solution to my problem of SUMIF Function with merged cells.. I need to find out total bonus earned by each employee during the years 2010-11, 2011-12, 2012-13, 2013-14..