我正在通过selenium网格运行selenium测试，但是当它执行tearDownAfterClass()方法时，会出现此问题：
com.thoughtworks.selenium.SeleniumException: Internal Server Error
at com.thoughtworks.selenium.HttpCommandProcessor.throwAssertionFailureExceptionOrError(HttpCommandProcessor.java:112)
at com.thoughtworks.selenium.HttpCommandProcessor.getCommandResponseAsString(HttpCommandProcessor.java:183)
at com.thoughtworks.selenium.HttpCommandProcessor.executeCommandOnServlet(HttpCommandProcessor.java:118)
at com.thoughtworks.selenium.HttpCommandProcessor.doCommand(HttpCommandProcessor.java:101)
at com.thoughtworks.selenium.HttpCommandProcessor.stop(HttpCommandProcessor.java:265)
at com.thoughtworks.selenium.DefaultSelenium.stop(DefaultSelenium.java:139)
at com.thoughtworks.selenium.grid.tools.ThreadSafeSeleniumSessionStorage.closeSeleniumSession(ThreadSafeSeleniumSessionStorage.java:33)
at com.icil.at.as.testtool.Suppliernamelookupv03Test.tearDownAfterClass(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:76)
at org.testng.internal.Invoker.invokeConfigurationMethod(Invoker.java:525)
at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:202)
at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:130)
at org.testng.internal.TestMethodWorker.invokeAfterClassMethods(TestMethodWorker.java:222)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:112)
at org.testng.TestRunner.runWorkers(TestRunner.java:1147)
at org.testng.TestRunner.privateRun(TestRunner.java:749)
at org.testng.TestRunner.run(TestRunner.java:600)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:317)
at org.testng.SuiteRunner.access$000(SuiteRunner.java:34)
at org.testng.SuiteRunner$SuiteWorker.run(SuiteRunner.java:351)
at org.testng.internal.thread.ThreadUtil$CountDownLatchedRunnable.run(ThreadUtil.java:147)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:636)
在我的测试脚本中，此方法如下：
@AfterClass
public static void tearDownAfterClass() throws Exception {
closeSeleniumSession();
}
有人建议使用selenium.cloce（），这个错误就消失了。但在我的脚本中，它使用Selenium网格。在我的脚本中，只有这一种方法失败了，其他方法都成功了。
有人可以帮我检查一下并告诉我它有什么问题吗？