Plug-in com.android.ide.eclipse.adt was unable to load class

Error
Mon Nov 17 11:14:00 CST 2014
Plug-in com.android.ide.eclipse.adt was unable to load class com.android.ide.eclipse.adt.internal.welcome.AdtStartup.


java.lang.ClassNotFoundException: An error occurred while automatically activating bundle com.android.ide.eclipse.adt (843).
	......
Caused by: org.osgi.framework.BundleException: Exception in com.android.ide.eclipse.adt.AdtPlugin.start() of bundle com.android.ide.eclipse.adt.
	... 26 more
Caused by: java.lang.NullPointerException
	... 33 moreError
Mon Nov 17 11:14:00 CST 2014
Plug-in c