Lookup issue returning odd results

[ExcelRoy]

Hi all,

I have the following LOOKUP formula

=IF(C3&I3="","",IFERROR(LOOKUP(9.99999999999999E+307,1/(($FL$3:$FL$10002=C3)*($FM$3:$FM$10002=I3)),$FO$3:$FO$10002),"Backorder"))

This seems to work most of the time but for some reason results "" when there is nothing found in FO3:FO10002
Sometimes it shows 00/01/1900 also

Is there a way to modify the formula to only show "Backorder" if nothing is found in FO3:FO10002

But retaining the =IF(C3&I3="","" part of the formula

Many thanks for any help

 

[ExcelRoy]

Perfect, thanks RoryA