Be more specific about what you have.  A row doesn't calculate anything, a
formula does.  What are the formulas you have?  In what cells/columns?  What
are in the other columns?  Check the formats in the cells of the various
columns.  A cell that is formatted as text will display a number if a number
is entered into it, but in fact Excel will take that number as text.  Any
subsequent calculations with that "number" will not be correct.  HTH  Otto

I would look at the two most likely sources of error:

1. A list of values was increased in size and the formula that referenced
the list was not updated to include the larger size

2. More likely - a value has been entered in a cell formatted for Text.  The
value LOOKS like good, but actually has the value 0.  Functions like

=SUM(A1:A100)

will not trap the error