Error when selecting CUSTOM TYPE in chart menu

Hello all.
I created a custom chart type for something I was tracking and all was well for several weeks. Then I started getting this message when I clicked on the CUSTOM TYPES tab in the chart setup menu to have the chart automatically formatted (see sheet 2 of the attached file for a screen shot of the error message). Sheet 1 of the attached file is the data I use in the chart. I suspect this has something to do with my Excel program / operating system so someone else would not get the error if they tried to create a chart with their Excel program.
If any of you have seen this error or know how to get rid of it, please let me know.

Thanks,
Numcruncher1