Eclipse java.lang.ClassNotFoundException: com.google.gwt.dev.About

I have a trouble with exception on importing (compiling) some GWT project into Eclipse.

My environment is

Mac OS X 1.6.2 Eclipse IDE for Java EE Developers 1.2.1.20090918-0703 epp.package.jee Google App Engine Java SDK 1.3.1 1.3.1.v201002101412 Google Web Toolkit SDK 2.0.3 2.0.3.v201002191036

Exception Stack
java.lang.ClassNotFoundException: com.google.gwt.dev.About
    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:315)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:250)
    at com.google.gwt.eclipse.core.runtime.GWTRuntime.getVersion(GWTRuntime.java:113)
    at com.google.gdt.eclipse.core.sdk.AbstractSdk.getDescription(AbstractSdk.java:53)
    at com.google.gdt.eclipse.core.sdk.SdkClasspathContainerInitializer.getDescription(SdkClasspathContainerInitializer.java:63)
    at com.google.gwt.eclipse.core.runtime.GWTRuntimeContainerInitializer.getDescription(GWTRuntimeContainerInitializer.java:43)
    at org.eclipse.jdt.internal.core.JavaModelManager.initializeContainer(JavaModelManager.java:2604)
    at org.eclipse.jdt.internal.core.JavaModelManager.getClasspathContainer(JavaModelManager.java:1778)
    at org.eclipse.jdt.core.JavaCore.getClasspathContainer(JavaCore.java:2652)
    at org.eclipse.jdt.internal.core.JavaProject.resolveClasspath(JavaProject.java:2578)
    at org.eclipse.jdt.internal.core.ClasspathEntry.validateClasspath(ClasspathEntry.java:1528)
    at org.eclipse.jdt.internal.core.ClasspathValidation.validate(ClasspathValidation.java:73)
    at org.eclipse.jdt.internal.core.DeltaProcessor.resourceChanged(DeltaProcessor.java:1994)
    at org.eclipse.jdt.internal.core.DeltaProcessingState.resourceChanged(DeltaProcessingState.java:470)
    at org.eclipse.core.internal.events.NotificationManager$2.run(NotificationManager.java:291)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.events.NotificationManager.notify(NotificationManager.java:285)
    at org.eclipse.core.internal.events.NotificationManager.broadcastChanges(NotificationManager.java:149)
    at org.eclipse.core.internal.resources.Workspace.broadcastBuildEvent(Workspace.java:297)
    at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:136)
    at org.eclipse.cor开发者_JAVA百科e.internal.events.AutoBuildJob.run(AutoBuildJob.java:238)
    at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

Session Data

eclipse.buildId=M20090917-0800
java.version=1.6.0_17
java.vendor=Apple Inc.
BootLoader constants: OS=macosx, ARCH=x86, WS=cocoa, NL=en_US
Framework arguments:  -product org.eclipse.epp.package.jee.product -keyring /Users/kanakohayashi/.eclipse_keyring -showlocation
Command-line arguments:  -os macosx -ws cocoa -arch x86 -product org.eclipse.epp.package.jee.product -keyring /Users/kanakohayashi/.eclipse_keyring -showlocation

Importing is not the same as compiling. Anyway, you need to associate your project with GWT. Have a look at http://code.google.com/webtoolkit/usingeclipse.html. It might be easier to import the code after creating a new project using this wizard via copy and paste :)