When I try to do a find and replace, I get the following message: "Formula
too long"

This is the formula in the cell. I am replacing $O$ with $X$

='[2005 Budget - Marketing.xls]2005 bgt by season'!$M$14+'[2005 Budget -
Marketing.xls]2005 bgt by season'!$O$14+'[2005 Budget - Marketing.xls]2005
bgt by season'!$M$15+'[2005 Budget - Marketing.xls]2005 bgt by
season'!$O$15+'[2005 Budget - Marketing.xls]2005 bgt by season'!$M$17+'[2005
Budget - Marketing.xls]2005 bgt by season'!$O$17+'[2005 Budget -
Marketing.xls]2005 bgt by season'!$M$71+'[2005 Budget - Marketing.xls]2005
bgt by season'!$O$71+'[2005 Budget - Marketing.xls]2005 bgt by
season'!$M$89+'[2005 Budget - Marketing.xls]2005 bgt by season'!$O$89+'[2005
Budget - Marketing.xls]2005 bgt by season'!$M$101+'[2005 Budget -
Marketing.xls]2005 bgt by season'!$O$101+'[2005 Budget - Marketing.xls]2005
bgt by season'!$M$110+'[2005 Budget - Marketing.xls]2005 bgt by
season'!$O$110+'[2005 Budget - Marketing.xls]2005 bgt by
season'!$M$124+'[2005 Budget - Marketing.xls]2005 bgt by
season'!$O$124+'[2005 Budget - Marketing.xls]2005 bgt by
season'!$M$153+'[2005 Budget - Marketing.xls]2005 bgt by season'!$O$153