step5.click();
Thread.sleep(50000);

// this is important part.
//System.out.println(driver.getCurrentUrl());
driver.context("WEBVIEW");
// driver.switchTo().window("WEBVIEW");
System.out.println(driver.getCurrentUrl());
Thread.sleep(20000);
driver.findElementById("login_email"); <----------代码到这里出错

org.openqa.selenium.WebDriverException: An unknown server-side error occurred while processing the command. (WARNING: The server did not provide any stacktrace information)
Command duration or timeout: 1.26 seconds
Build info: version: '2.42.2', revision: '6a6995d31c7c56c340d6f45a76976d43506cd6cc', time: '2014-06-03 10:52:47'
System info: host: 'PC-20140519QFMN', ip: '172.20.1.58', os.name: 'Windows 7', os.arch: 'amd64', os.version: '6.1', java.version: '1.8.0_05'
Driver info: io.appium.java_client.AppiumDriver
Capabilities [{appPackage=com.gamelala.android.trivialdrivesample, warnings={}, databaseEnabled=false, deviceName=Android Emulator, platform=LINUX, appActivity=.DemoActivity, desired={appPackage=com.gamelala.android.trivialdrivesample, appActivity=.DemoActivity, platformVersion=4.4.2, browserName=, platformName=Android, deviceName=Android Emulator}, platformVersion=4.4.2, webStorageEnabled=false, browserName=, takesScreenshot=true, javascriptEnabled=true, platformName=Android}]
Session ID: e374d3f2-da5a-4b4a-b815-7bf560d920ff
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:204)
at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:156)
at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:599)
at io.appium.java_client.AppiumDriver.execute(AppiumDriver.java:95)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:352)
at org.openqa.selenium.remote.RemoteWebDriver.findElementByCssSelector(RemoteWebDriver.java:441)
at org.openqa.selenium.By$ByCssSelector.findElement(By.java:425)
at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:344)
at Gamelala_01.GL_PAY.MainProcess.a_Paypal_Ts(MainProcess.java:93)
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 org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)