This is probably due to a numerical value that is coded as a factor. Have a
look at the example below.

> In ggplot2 one line per group is plotted. The default grouping is the
> combination of all factors. In the first example only B, in the second and
> third example both A and B. This leaves just one observation per group and
> hence the line cannot be displayed.
>
>
You got that right Thierry. Year was char , on conversion to numeric I CAN
see the lines. Many thanks to all of you guys: Sarah, Hadley and Thierry.

I changed from desktop to my laptop hence the  64 bit to 32 bit.

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