I cannot believe you want to replace all blanks in a file with a value.
Each worksheet has 16,777,216 cells
That would make for a very large workbook.
Are you saying you have formulas like =IF(A1<>15, "",A15) that return "" which
is not null but just looks blank?
If not, what?
Post your IF function formula and is it representative of other formulas?
Gord