Plotting box plots with numeric, not categorical, x-axis data

Hello,

I am trying to make a box plot. I have gone through the Box Plot Demo and this all went fine. However, when trying to plot my own from a freshly created table I get strange results. Unlike (seemingly) the Demo dataset, my x-axis data are not categorical but numeric (geological age in millions of years) and I wonder if it is the data type that is hindering my success. Any advice would be greatly appreciated.

Regards
Russ