i had a cell (C1) called "total" that displays the sum of two other cells..
i.e. the total cell got the formula "=sum(A1+B1)" ..

I then typed a value in cell (D1). Then I tried to add C1 to D1 in the cell
E1. I used segma sign to add the two cells(C1+D1)
or I typed the formula "=sum(C1+D1)" in the cell E1. However, the cell E1
gave a "Value!" error.

I don't know why..

when I tried the same in another computer, it worked well

I wonder if there is options to make the cell E1 show the result.