java.lang.NullPointerException gor Groovy Script

we are load testing the webservice using "soapUI-Pro". due to unavailability of complete information in User Guide about Groovy script and the global files we are facing issue.

We tried to import test data(i.e year) using Excel-->Property Transfer-->Request-->Property Transfer-->Log Groovy-->Show result Groovy-->data Sink-->Loop.

My scripts is failing in Show result Groovy.

Ansd wehn i do a load test the whole script is failing and the error message from the error log is as follows:

"2008-05-08 11:46:44,147 ERROR [errorlog] java.lang.NullPointerException
java.lang.NullPointerException
at jxl.write.biff.File.write(File.java:147)
at jxl.write.biff.WritableWorkbookImpl.write(WritableWorkbookImpl.java:697)
at com.eviware.soapui.impl.wsdl.teststeps.datasink.ExcelDataSink.finish(SourceFile:159)
at com.eviware.soapui.impl.wsdl.teststeps.WsdlDataSinkTestStep.finish(SourceFile:192)
at com.eviware.soapui.impl.wsdl.testcase.WsdlTestCaseRunner.run(WsdlTestCaseRunner.java:262)
at com.eviware.soapui.impl.wsdl.loadtest.WsdlLoadTestRunner$TestCaseRunner.run(WsdlLoadTestRunner.java:401)
at java.lang.Thread.run(Unknown Source)"

I really dont understand whether i'm missing any .jar files or missing from soapUI-Pro end

Attaching my Project file as well for your reference.

Any replies are appreciated.

Thanks in advance