Excel addition formula results in 0

[GLSmith06]

I have a summary worksheet showing currency sums from other worksheets in the file.

When I try to do addition of various cells such as:   =E51+M51+P51 the result shows as a 0

Each of those cells shows a positive number that is not zero

The row above uses the same formula =E50+M50+P51 and shows a proper sum

This seems to be a recent problem 

I have run error check and do not seem to be able to find any problems in my formulas or data

any ideas?

[#2]

@GLSmith06 

Make sure that E51, M51 and P51 are real numbers and not text values that look like numbers.