COUNTA calculation - Formula in cell refers to arange with additional numbers adjacent?

Hi,

I am facing a problem with one of my formulas. I have a workbook with the months in N13:Y13 and Year to date colum in AA13. Colum A16:A113 contains accountlines with the respective values for the individual months of the year.

I would like to calculate a run-rated Full Year 2012 value based on the months but not manually amend the formula during the year. I use COUNTA in order to achieve that.

=IF(ISERROR(AA16/COUNTA(N16:S16)*12),"-",AA16/COUNTA(N16:S16)*12)

The formula seems not to calculate correctly and when pointing at the cell Excel tells me: "The formula in this cell refers to a range that has additional number adjacent to it."

I have played around with the Error checking in Tools-->Options, but could not find a solution. Why is this calculation not performing correctly and is there a way to solve this or a smarter way to calculate?

Many thanks!

Dilipandey, thanks for your reply. I tried it again and you are right it does calculate correctly. Slightly embarrassed....

Thanks though for looking into this.