Error while running groovy script - Illegal XML character: 0

soapUI Pro 4.5.1,
copyright (C) 2007-2012
smartbear.com
http://www.soapui.org | http://smartbear.com
Build [internal], Build Date 2012/06/27 14:05

Groovy script:

def groovyUtils = new com.eviware.soapui.support.GroovyUtils( context );
def holder = groovyUtils.getXmlHolder("{TestStepName}#response");
log.info holder['//data']

Problem:

My groovy script works fine most of the times, but every now and then I get the following error message

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org.apache.xmlbeans.XmlException: error: Illegal XML character: 0x0 org.apache.xmlbeans.impl.piccolo.io.IllegalCharException: Illegal XML character: 0x0 at org.apache.xmlbeans.impl.piccolo.xml.XMLReaderReader.read(XMLReaderReader.java:169) at org.apache.xmlbeans.impl.piccolo.xml.PiccoloLexer.yy_refill(PiccoloLexer.java:3474) at org.apache.xmlbeans.impl.piccolo.xml.PiccoloLexer.yylex(PiccoloLexer.java:3958) at org.apache.xmlbeans.impl.piccolo.xml.Piccolo.yylex(Piccolo.java:1290) at org.apache.xmlbeans.impl.piccolo.xml.Piccolo.yyparse(Piccolo.java:1400) at org.apache.xmlbeans.impl.piccolo.xml.Piccolo.parse(Piccolo.java:714) at org.apache.xmlbeans.impl.store.Locale$SaxLoader.load(Locale.java:3454) at org.apache.xmlbeans.impl.store.Locale.parse(Locale.java:712) at org.apache.xmlbeans.impl.store.Locale.parseToXmlObject(Locale.java:696) at org.apache.xmlbeans.impl.store.Locale.parseToXmlObject(Locale.java:683) at org.apache.xmlbeans.impl.schema.SchemaTypeLoaderBase.parse(SchemaTypeLoaderBase.java:208) at org.apache.xmlbeans.XmlObject$Factory.parse(XmlObject.java:580) at com.eviware.soapui.support.xml.XmlUtils.createXmlObject(XmlUtils.java:263) at com.eviware.soapui.support.XmlHolder. (XmlHolder.java:38) at com.eviware.soapui.support.XmlHolder. (XmlHolder.java:54) at com.eviware.soapui.support.GroovyUtils.getXmlHolder(GroovyUtils.java:72) at com.eviware.soapui.support.GroovyUtils$getXmlHolder.call(Unknown Source) at Script2.run(Script2.groovy:2) at com.eviware.soapui.support.scripting.groovy.SoapUIGroovyScriptEngine.run(SoapUIGroovyScriptEngine.java:96) at com.eviware.soapui.support.scripting.groovy.SoapUIProGroovyScriptEngineFactory$SoapUIProGroovyScriptEngine.run(SourceFile:89) at com.eviware.soapui.impl.wsdl.teststeps.WsdlGroovyScriptTestStep.run(WsdlGroovyScriptTestStep.java:149) at com.eviware.soapui.impl.wsdl.panels.teststeps.GroovyScriptStepDesktopPanel$RunAction$1.run(GroovyScriptStepDesktopPanel.java:274) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) error at line: 2

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Can anyone suggest on how to resolve this?
At times a property transfer step (to transfer response value) before calling the script seems to resolve the issue.

Thanks!