Excel 2002 SP3.

This maybe a stupid question (I'm not a statistician or mathematician).

I have data that looks like this:

Na 0.032617
Cl 0.0265
Ca 0.000524
K 0.005523
Mg 0.0000823
PO4 0.00031
HCO3 0.001655

I am plotting it with categorical values on the xaxis and the numerical
value on the y axis. I am using a logarithmic scale for the y axis.

I am getting the "Negative or zero values cannot be plotted correctly
on log charts. Only positive values can be interpreted on a
logarithmic scale" message, which I see from the newsgroup is common if
there are zeros in the data. However, the data I am using does not
appear to be zero to me. All the numbers are positive, even if they
are small.

So why am I getting this message?

Thank you.
Nicole