Maximum number of ranges in an Excel 2010 line graph?

I've got an Excel 2010 line graph with 20 different ranges, plus the X-axis.

It works just fine with 20 ranges, but it doesn't seem to want me to add a 21st range. At any rate, the 21st range won't display on the graph. Is 20 the maximum number of displayable ranges in an Excel line graph? Or is something else wrong?

I've been trying to attach a .jpg or a .pdf, to no avail. I'll again try to attach them just before I post.Recid-2015-Apr.jpgRecid-2015-Apr.pdf