What is this mean: com.thoughtworks.selenium.SeleniumException: ERROR: Selenium failure. Please report to the Selenium Users forum at http://forums.openqa.org, with error details from the log window. The error message is: openedWindow has no properties?

[Xiaojun,Wei]

Hello,
I used Firefox and JAVA.
Yesterday words My Program with waitForPageToLoad() very well.
Today i have run my Programm again, there is Erro:
com.thoughtworks.selenium.SeleniumException: ERROR: Selenium failure. Please report to the Selenium Users forum at http://forums.openqa.org, with error details from the log window. The error message is: openedWindow has no properties\\ at com.thoughtworks.selenium.HttpCommandProcessor.doCommand(HttpCommandProcessor.java:73)\\ at com.thoughtworks.selenium.DefaultSelenium.click(DefaultSelenium.java:82)\\ at de.mms_dresden.tsi.Versuch10webSeit12.deep10Test(Versuch10webSeit12.java:338)\\ at de.mms_dresden.tsi.Versuch10webSeit12.deep10Test(Versuch10webSeit12.java:387)\\ at de.mms_dresden.tsi.Versuch10webSeit12.testNew(Versuch10webSeit12.java:435)\\ at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)\\ at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)\\ at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)\\ at java.lang.reflect.Method.invoke(Unknown Source)\\ at junit.framework.TestCase.runTest(TestCase.java:168)\\ at junit.framework.TestCase.runBare(TestCase.java:134)\\ at com.thoughtworks.selenium.SeleneseTestCase.runBare(SeleneseTestCase.java:71)\\ at junit.framework.TestResult$1.protect(TestResult.java:110)\\ at junit.framework.TestResult.runProtected(TestResult.java:128)\\ at junit.framework.TestResult.run(TestResult.java:113)\\ at junit.framework.TestCase.run(TestCase.java:124)\\ at junit.framework.TestSuite.runTest(TestSuite.java:232)\\ at junit.framework.TestSuite.run(TestSuite.java:227)\\ at org.junit.internal.runners.OldTestClassRunner.run(OldTestClassRunner.java:76)\\ at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:38)\\ at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)\\ at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)\\ at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)\\ at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)\\ at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

What's that mean? i have changed nothing in my Programm, i'm afrai, is there something wrong in Firefox?
Help! Help! Help!

[Xiaojun,Wei]

hello,
Everyone,
The origin, why i have a ERROR: Selenium failure, ist in my Firefox, i have blocked the Pop-Ups.
When i allow this Pop-Ups, i have the trouble no more.