index/match search works in some cells, but not others?

I have a spreadsheet set up where two companies share various expenses for 10 months, then one company pays all expenses for the last two months of the year. To fill in some of the expenses, I'm using an index/match search to match both the type of expense and the month. Unfortunately, the formula works in one cell, but no others. This is the original formula? The working formula is in cell K3; it picks up the value from the table in the lower left perfectly fine.

However, when I copy the formula into the cell below it, it doesn't work. Once I copy it into the cell that should match January's expenses, I get an error. This is the original formula:

=IF(OR($B3="June",$B3="July"),0,INDEX($C$24:$G$35,MATCH($K$1,$C$23:$G$23,0),MATCH($B3,$B$24:$B$35,0))/2)

and it's copied into the cells below it. See the attached spreadsheet for more information. What's the problem with this? I'm pulling my hair out trying to see the problem with the formula!

Thank you!