myeclipse.exe启动不了，日志中显示此错误，怎么解决？

点击myeclipse.exe启动不了，日志中显示此错误：
!SESSION Sat May 25 09:05:09 CST 2013 ------------------------------------------
!ENTRY org.eclipse.equinox.launcher 4 0 2013-05-25 09:05:09.575
!MESSAGE Exception launching the Eclipse Platform:
!STACK
java.lang.ClassNotFoundException: org.eclipse.core.runtime.adaptor.EclipseStarter
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:556)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
at org.eclipse.equinox.launcher.Main.run(Main.java:1311)