Setting values for "TRUE","FALSE" and "#REF!"

Hi everybody

Im working on a worksheet where i wanna check cells in two other types of work sheets but but only one of the exists for each number.

Ive made this cell: "=IF(OR(SUM(INDIRECT("'[Kreditor mappe "&B9&".xls]Løndebitorer'!$L:$L"))+SUM(INDIRECT("'[Kreditor mappe "&B9&".xls]Ferieval.'!$L$1:$L$40"))>0;SUM(INDIRECT("'[Debitor mappe "&B9&".xls]Løndebitorer'!$L:$L"))+SUM(INDIRECT("'[Debitor mappe "&B9&".xls]Ferieval.'!$L$1:$L$40"))>0);1;0)" but of course i get #REF! because one of the files are missing, i want to know how i can set #REF!=0.

I really hope theres a hardcore excel user out there that can help me

-Hurtige

EDIT: changed the cell function.