You have two choices. First, you can provide your own labels, using empty strings in the case of 0% and NaN.
e.g.:
<code>
//Make the series use the custom label
bar1.DataLabels.Format = "<label>";
//provide the labels
bar1.Labels.Add( "20" );
bar1.Labels.Add( "" );
bar1.Labels.Add( "40" );
bar1.Labels.Add( "50" );
</code>.
Second, you can use a subset of the labels, by indicating to the chart the index of the points you want to use.
e.g.:
<code>
//create the subset and provide the indexes
DataSeriesSubset subset = new DataSeriesSubset();
subset.AddIndex( 0 );
subset.AddIndex( 2 );
//set the series appropriately
bar.DataLabels.Mode = DataLabelsMode.Subset;
bar.DataLabels.Subset = subset;
</code>
André
Software Developer and Tech Support
Xceed Software Inc.