Errors migrating to GWT 2.7.0 . Can someone please help me ?

I am getting the following error while performing Ant Build.
Can someone please help me ?

Compiling module com.acg.mmsea.gwt.Appname
     [java]    [WARN] Unable to read: jar:file:/C:/gwt-2.7.0/gwt-user.jar!/com/google/gwt/core/Core.gwtar. Skipping: java.io.InvalidClassException: com.google.gwt.dev.jjs.SourceOrigin$1; local class incompatible: stream classdesc serialVersionUID = -2407201776821563037, local class serialVersionUID = 4713379764594032837
     [java]    [WARN] Unable to read: jar:file:/C:/gwt-2.7.0/gwt-user.jar!/com/google/gwt/user/User.gwtar. Skipping: java.io.InvalidClassException: com.google.gwt.dev.jjs.SourceOrigin$1; local class incompatible: stream classdesc serialVersionUID = -2407201776821563037, local class serialVersionUID = 4713379764594032837
     [java]    [WARN] Unable to read: jar:file:/C:/gwt-2.7.0/gwt-user.jar!/com/google/gwt/user/UI.gwtar. Skipping: java.io.InvalidClassException: com.google.gwt.dev.jjs.SourceOrigin$1; local class incompatible: stream classdesc serialVersionUID = -2407201776821563037, local class serialVersionUID = 4713379764594032837
     [java]    [WARN] Unable to read: jar:file:/C:/gwt-2.7.0/gwt-user.jar!/com/google/gwt/user/DOM.gwtar. Skipping: java.io.InvalidClassException: com.google.gwt.dev.jjs.SourceOrigin$1; local class incompatible: stream classdesc serialVersionUID = -2407201776821563037, local class serialVersionUID = 4713379764594032837
     [java]    [WARN] Unable to read: jar:file:/C:/gwt-2.7.0/gwt-user.jar!/com/google/gwt/user/RemoteService.gwtar. Skipping: java.io.InvalidClassException: com.google.gwt.dev.jjs.SourceOrigin$1; local class incompatible: stream classdesc serialVersionUID = -2407201776821563037, local class serialVersionUID = 4713379764594032837
     [java]    [WARN] Unable to read: jar:file:/C:/gwt-2.7.0/gwt-user.jar!/com/google/gwt/xml/XML.gwtar. Skipping: java.io.InvalidClassException: com.google.gwt.dev.jjs.SourceOrigin$1; local class incompatible: stream classdesc serialVersionUID = -2407201776821563037, local class serialVersionUID = 4713379764594032837
     [java]    Ignored 2 units with compilation errors in first pass.

[ERROR] Unexpected internal compiler error
     [java] java.lang.RuntimeException: Unexpected IOException on in-memory stream
     [java]     at com.google.gwt.dev.javac.CompilationUnit.getTypes(CompilationUnit.java:383)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.assimilateSourceUnit(UnifyAst.java:999)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.internalFindType(UnifyAst.java:1595)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.translate(UnifyAst.java:1653)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.translate(UnifyAst.java:1645)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.resolveType(UnifyAst.java:1552)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.assimilateSourceUnit(UnifyAst.java:1010)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.internalFindType(UnifyAst.java:1595)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.translate(UnifyAst.java:1653)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.translate(UnifyAst.java:1645)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.resolveType(UnifyAst.java:1552)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.assimilateSourceUnit(UnifyAst.java:1010)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.internalFindType(UnifyAst.java:1595)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.translate(UnifyAst.java:1653)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.translate(UnifyAst.java:1645)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.resolveType(UnifyAst.java:1552)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.assimilateSourceUnit(UnifyAst.java:1010)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.internalFindType(UnifyAst.java:1595)
     [java]     at com.google.gwt.dev.jjs.impl.UnifyAst.addRootTypes(UnifyAst.java:733)
     [java]     at com.google.gwt.dev.jjs.JavaToJavaScriptCompiler$Precompiler.unifyJavaAst(JavaToJavaScriptCompiler.java:1291)
     [java]     at com.google.gwt.dev.jjs.JavaToJavaScriptCompiler$Precompiler.constructJavaAst(JavaToJavaScriptCompiler.java:1038)
     [java]     at com.google.gwt.dev.jjs.JavaToJavaScriptCompiler$Precompiler.precompile(JavaToJavaScriptCompiler.java:954)
     [java]     at com.google.gwt.dev.jjs.MonolithicJavaToJavaScriptCompiler.precompile(MonolithicJavaToJavaScriptCompiler.java:303)
     [java]     at com.google.gwt.dev.jjs.JavaScriptCompiler.precompile(JavaScriptCompiler.java:38)
     [java]     at com.google.gwt.dev.Precompile.precompile(Precompile.java:286)
     [java]     at com.google.gwt.dev.Precompile.precompile(Precompile.java:229)
     [java]     at com.google.gwt.dev.Precompile.precompile(Precompile.java:145)
     [java]     at com.google.gwt.dev.Compiler.run(Compiler.java:206)
     [java]     at com.google.gwt.dev.Compiler.run(Compiler.java:158)
     [java]     at com.google.gwt.dev.Compiler$1.run(Compiler.java:120)
     [java]     at com.google.gwt.dev.CompileTaskRunner.doRun(CompileTaskRunner.java:55)
     [java]     at com.google.gwt.dev.CompileTaskRunner.runWithAppropriateLogger(CompileTaskRunner.java:50)
     [java]     at com.google.gwt.dev.Compiler.main(Compiler.java:127)
     [java] Caused by: java.io.InvalidClassException: com.google.gwt.dev.jjs.SourceOrigin$1; local class incompatible: stream classdesc serialVersionUID = -2407201776821563037, local class serialVersionUID = 4713379764594032837
     [java]     at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:619)
     [java]     at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1606)
     [java]     at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1501)
     [java]     at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1755)
     [java]     at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1334)
     [java]     at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1976)
     [java]     at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1900)
     [java]     at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1782)
     [java]     at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1334)
     [java]     at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1976)
     [java]     at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1900)
     [java]     at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1782)
     [java]     at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1334)
     [java]     at java.io.ObjectInputStream.readObject(ObjectInputStream.java:353)
     [java]     at java.util.ArrayList.readObject(ArrayList.java:731)
     [java]     at sun.reflect.GeneratedMethodAccessor23.invoke(Unknown Source)
     [java]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     [java]     at java.lang.reflect.Method.invoke(Method.java:600)
     [java]     at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1028)
     [java]     at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1878)
     [java]     at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1782)
     [java]     at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1334)
     [java]     at java.io.ObjectInputStream.readObject(ObjectInputStream.java:353)
     [java]     at com.google.gwt.dev.jjs.ast.JDeclaredType.readMembers(JDeclaredType.java:412)
     [java]     at com.google.gwt.dev.jjs.ast.JProgram.deserializeTypes(JProgram.java:229)
     [java]     at com.google.gwt.dev.javac.CompilationUnit.getTypes(CompilationUnit.java:381)
     [java]     ... 32 more

BUILD FAILED
C:\APPNAME WrkSpc\AppName\build.xml:65: Java returned: 1

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