Error Message: Run-time error '1004':

I've been using a conditional formula and have had no problems with the worksheet until recently. When I select the cell to place the sum of the "conditional sum formula" I get this error message: Run-time error '1004': Unable to set the FormulaArray property of the Range class.

What does this mean? Is the worksheet corrupted or is there a way around this?

Do you have some worksheet event code? If so, show it.