[#3104] - Adding Label Expression for Chart Data throws Java Error " Error filling print... java.lang.Long cannot be cast to java.lang.String"

The report encounters the following error on executing a report with chart. This happens when you define label expression for the chart. Please see attached screenshot (scr1.jpg).

java.lang.Exception: 1 - java.lang.Long cannot be cast to java.lang.String      at com.jaspersoft.ireport.jasperserver.ws.WSClient.runReport(WSClient.java:403)      at com.jaspersoft.ireport.jasperserver.ws.WSClient.runReport(WSClient.java:320)      at com.jaspersoft.ireport.jasperserver.ReportRunner.run(ReportRunner.java:70)      at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:572)      at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:997)