Only single field allowed for this chart type

May occur when setting up charts for a report

May occur when settings up charts in summaries

If the Chart type is a Pie chart only one field (column) can chosen. The pie chart shows the distribution of that field over the items in the summary.

For example, at the Part Summary a pie chart may show the Material cost for each material used based on sub totals.

The pie chart shows the sub total for each material visually. It does not make sense to choose more than one field at a time for Pie charts.

Check the chart settings