What's the value in that cell? (for you to know which cell has the
faulty result try in the immediate window this (once the row gets
highlighted in yellow, the error fires and you click on debug)
?onecell.address (and then hit enter) - it will give you the address
of the cell that's wrong.
There would be an error, I guess - i.e., the cell value isn't blank
and isn't a number and isn't a text but it's something like
!DIVO
#NA
or any other similar error.
If you fix the formula not to show errors, it should be fine.
In the meantime if the onecell value isn't error - post back.