You are trying to change the data in the {Current Month} range to s specific month?

Oh. In that case you want to adjust your criteria and not the data within the range. To do that, you would change the criteria to the month number you want to search for.

=SUMIFS({Error Cost}, {Error Code}, $[Primary Column]@row, {Location}, [Column2]$1, {Current month}, =MONTH($[Column9]$26))

For June:

=SUMIFS({Error Cost}, {Error Code}, $[Primary Column]@row, {Location}, [Column2]$1, {Current month}, = 6)

For July:

=SUMIFS({Error Cost}, {Error Code}, $[Primary Column]@row, {Location}, [Column2]$1, {Current month}, = 7)

Are you able to copy/paste the exact formula that is causing the error directly from the sheet to here? The formula I provided shouldn't be throwing that error.