Custom XML Report: java.sql.SQLException: ORA-01427: single-row subquery returns more than one row

A custom developed XML report is returning the following error:

--SQLException
java.sql.SQLException: ORA-01427: single-row subquery returns more than one row

	at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:462)
	at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:405)
	at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:931)
	at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:481)
	at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:205)
	at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:548)
	at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:217)
	at oracle.jdbc.driver.T4CPreparedStatement.executeForDescribe(T4CPreparedStatement.java:947)
	at oracle.jdbc.driver.OracleStatement.executeMaybeDescribe(OracleStatement.java:1283)
	at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1441)
	at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:3769)
	at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:3823)
	at oracle.jdbc.driver.OraclePreparedStatementWrapper.executeQuery(OraclePreparedStatementWrapper.java:1671)
	at oracle.apps.xdo.dataengine.XMLPGEN.processQuery(Unknown Source)
	at oracle.apps.xdo.dataengine.XMLPGEN.processSQLDataSource(Unknown Source)
	at oracle.apps.xdo.dataengine.XMLPGEN.writeData(Unknown Source)
	at oracle.apps.xdo.dataengine.XMLPGEN.writeGroupStructure(Unknown Source)
	at oracle.apps.xdo.dataengine.XMLPGEN.processData(Unknown Source)
	at oracle.apps.xdo.dataengine.XMLPGEN.processXML(Unknown Source)
	at oracle.apps.xdo.dataengine.XMLPGEN.writeXML(Unknown Source)
	at oracle.apps.xdo.dataengine.DataProcessor.processDataStructre(Unknown Source)
	at oracle.apps.xdo.dataengine.DataProcessor.processData(Unknown Source)
	at oracle.apps.xdo.oa.util.DataTemplate.processData(DataTemplate.java:350)
	at oracle.apps.xdo.oa.cp.JCP4XDODataEngine.runProgram(JCP4XDODataEngine.java:311)
	at oracle.apps.fnd.cp.request.Run.main(Run.java:159)

CP main completed runProgram for oracle.apps.xdo.oa.cp.JCP4XDODataEngine