CF Report - Graphing Problem

I am working in my first report with CF Report Builder, nice tool. Am getting this error after adding a simple pie chart.

Report data binding error Error evaluating expression : image_1 Source text : Report.GetChartData_0(query, calc, param). The chart could not be generated due to an error in the graphing engine.

Without the chart, the report generates correctly.

Please advise. Thank you.