What is wrong with the =SUM() function in Calc?

To whom this may concern:

I am an Ubuntu Linux user, and my default office suite is LibreOffice. I ran into a strange issue with 4.2.8 of LibreOffice, where the =SUM() function would not work. I would either receive the ### error or I would see something like =SUM(A1:B1) in the cell I was attempting to calculate in. I found that LibreOffice had recently updated, so I removed 4.2.8 from my computer, and installed 5.0.X. I am still experiencing the same problem with the newer version. Can someone please help me resolve this issue? I like to use Calc when I am calculating the cost of projects, and the =SUM() function not working is an issue because it will not add up my totals. Thank you.

The ### may simply be the column is not wide enough to display the result. Seeing the underlying formula in the formula bar is normal (the cell should show the ANSWER to the formula displayed in the formula bar). If the cell is displaying the formula instead of the result you may have your options (in Windows OPTIONS/LIBREOFFICE_CALC/VIEW, probably the same or very similar in Ubuntu) set to display formulas.