Indirect array versus named array formula problem

[Kris with a K]

Hi folks,

I have written some indirect formula functions such as the ones below.

=(SUMIF('OPWL (ret)'!$AG:$AG,CONCATENATE($C15," - ",D$6),INDIRECT("'OPWL (ret)'!$AH$2:$AH"&'OP Activity FS'!$C$12))+SUMIF('OPWL (ret2)'!$AG:$AG,CONCATENATE($C15," - ",D$6),INDIRECT("'OPWL (ret2)'!$AH$2:$AH"&'OP Activity FS'!$D$12)))*D$10

Isolating part of the formula...

=(SUMIF('OPWL (ret)'!$AG:$AG,CONCATENATE($C15," - ",D$6),INDIRECT("'OPWL (ret)'!$AH$2:$AH"&'OP Activity FS'!$C$12))

If 'OP Activity FS'$C$12 = 4000 then the result should be a sum of where the critera = the values in "AH2:AH4000"

The problem i am having is if there is 4000 rows in which to look the formual result is different if the indirect funcion is used to name the last row compared to removing the indirect funtion and summing "AH:AH" as an entire column

Does anybody know why this is happening and what to do to counter the problem.

I think i have laid out enough information to discribe the problem but let me know if you anyone needs more information.

Thanks in anticipation of your help.