Getting null pointer exception consistently

Hi, I am using SoapUI for security scan of RESTful web service.
For HTTPS POST request.
After running 2 or 3 scans, in SQL Injection or in Invalid Types, I get null pointer exception.

Here are the logs:
Tue Mar 26 14:59:23 IST 2013:ERROR:An error occured [java.lang.NullPointerException], see error log for details
Tue Mar 26 14:59:58 IST 2013:ERROR:An error occured [java.lang.NullPointerException], see error log for details
Tue Mar 26 14:59:58 IST 2013:ERROR:An error occured [java.lang.NullPointerException], see error log for details
Tue Mar 26 14:59:58 IST 2013:ERROR:An error occured [java.lang.NullPointerException], see error log for details
Tue Mar 26 14:59:58 IST 2013:ERROR:Exception during Test Execution
java.lang.NullPointerException
at com.eviware.soapui.security.result.SecurityScanResult.addSecurityRequestResult(SecurityScanResult.java:154)
at com.eviware.soapui.security.scan.AbstractSecurityScan.run(AbstractSecurityScan.java:220)
at com.eviware.soapui.security.SecurityTestRunnerImpl.runTestStepSecurityScan(SecurityTestRunnerImpl.java:302)
at com.eviware.soapui.security.SecurityTestRunnerImpl.runCurrentTestStep(SecurityTestRunnerImpl.java:212)
at com.eviware.soapui.security.SecurityTestRunnerImpl.runCurrentTestStep(SecurityTestRunnerImpl.java:39)
at com.eviware.soapui.impl.wsdl.support.AbstractTestCaseRunner.internalRun(AbstractTestCaseRunner.java:148)
at com.eviware.soapui.impl.wsdl.support.AbstractTestCaseRunner.internalRun(AbstractTestCaseRunner.java:43)
at com.eviware.soapui.impl.wsdl.support.AbstractTestRunner.run(AbstractTestRunner.java:135)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)


I am running SoapUI on MAC OSX 10.6.8
JAVA is java version "1.6.0_43"
Java(TM) SE Runtime Environment (build 1.6.0_43-b01-447-10M4203)
Java HotSpot(TM) 64-Bit Server VM (build 20.14-b01-447, mixed mode)

SoapUI version is 4.5.1

I have disabled broswer component, since it was making SoapUI hang.

I also tried latest nightly build [http://www.soapui.org/Downloads/soapui-nightly-builds.html]
But it was of no use.

Please help me. Let me know if there is any work around.