SUMIF and LEFT and Named Ranges
 

I have two named ranges in a table, 'AccNo' and 'AugustP'. Both
ranges are equal in length and occupy the same rows. 'AccNo' may have
the same value in more than one cell in the range.
My formula, =-SUMIF(AccNo,$B6,AugustP) works well where cell B6 equals
a cell in the named range 'AccNo', typically the number 5000.
I want to change the value of those cells in 'AccNo' with a text value
of say 5000-01, keep the value in B6 and still retain the value
produced by the original formula.
I have tried the formula =-SUMIF(LEFT(AccNo,4),$B6,AugustP) but Excel
tells me there is an error in the formula. I have made sure the cells
in 'AccNo' and B6 are formatted as text.
Has anybody any suggestions?
Thanks for any help offered,
Dave Moore