Inherited module error after adding GXT? - NoClassDefFoundError: com/google/gwt/core/ext/Generator?

I am using GWT 2.5

GXT 2.5.1

App Engine 1.9.0

I am getting this error.

Loading modules
   com.java.operastar.Opera_Star
      Loading inherited module 'com.java.operastar.Opera_Star'
         Loading inherited module 'com.extjs.gxt.ui.GXT'
            [ERROR] Unexpected error while processing XML
java.lang.NoClassDefFoundError: com/google/gwt/core/ext/Generator
    at java.lang.ClassLoader.findBootstrapClass(Native Method)
    at java.lang.ClassLoader.findBootstrapClassOrNull(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at com.google.gwt.dev.cfg.ModuleDefSchema$ClassAttrCvt.convertToArg(ModuleDefSchema.java:884)
    at com.google.gwt.dev.util.xml.HandlerArgs.convertToArg(HandlerArgs.java:64)
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Can anybody help to solve this. Screen short

Solution

Most probably the issue is due to version mismatch between GWT and GXT.

Try any one option:

try with GWT 2.5.0 and GXT.2.2.1 as shown in screenshot

enter image description here

use below inherits in gwt.xml as shown in screenshot also

<inherits name='com.sencha.gxt.ui.GXT' />

instead of

<inherits name="com.extjs.gxt.ui.GXT" />

enter image description here

--EDIT--

Whenever you change the dependencies or GWT version. Just delete the last auto-generated stub as shown in below screenshot and re-compile the project again. A fresh start.

enter image description here