Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
The product of the number of items in all column fields in a PivotTable cannot exceed 32,768.
This statement is taken from a Microsoft page athttp://support.microsoft.com/kb/211517
Of course, you may not be using a Pivot Table to store the values you are plotting. If you were, then you might be only limited to 10,000 x 3 which surely isn't the case.
However, the worksheet itself in Excel 2000 is limited to 256 rows. I think that explains the limitation. And that statement is taken from the same page cited above.
Supposedly, even without upgrading from Microsoft Excel 2000, you can escape these limitations by using server page fields. See the link from the cited page.
Please rate my Answer - favorably I would expect, since the data is accurate and a means of escaping the limitation is indicated - so that I may be paid for the work I have done on your question and case. Thanks.