Help with INDEX Formula

[Frick]

I have the following formula in cell WRKSHT_Mthly!AN53:

={IF(AN31=0,0,((DataInput!$C$79*1000*(DataInput!$O$78/12))*(INDEX(Production
_Sch1!$D$43:$GM$43,MATCH(YEAR(WRKSHT_Mthly!AN$3),YEAR(Production_Sch1!$D$4:$
GM$4),0)))))}

The problem is the formula is returning a -0- when it should be returning a
value. The formula is copied across col's and it is working properly except
in this col and the col preceding.

Here are the references:

AN31 =1 or 0 In this col it equals 1
DataInput!C79 =1.25
DataInput!O78=8,000
Production_Sch1!D43:GM43 have values of 1 or 0
WRKSHT!AN3 = First day of Month, which is a formula that takes the preceding
EOMONTH +1
Production_Sch1!D4:GM4 = Last Day of Month Date, which is the formula
EOMONTH(1st day,0)

The col's in question AN and 6 previous col's all are returning 0 and all
col's after are returning values as they should. The sttrange thing is that
col AN is Dec 06 and the previous cols Nov, Oct etc.

I've broken down the formula and when I do so it returns a value. Can
someone please explain what I am doing wrong here. It just makes no sense
and I've looked at this for over 2 hours now and can't figure out what's
wrong.

Thanks