The workspace exited with unsaved changes in the previous session; refreshing workspace to recover changes

eclipse.buildid=i20100608-0911

java.version=1.6.0_18

java.vendor=sun microsystems inc.

bootloader constants: os=win32, arch=x86, ws=win32, nl=zh_cn

framework arguments:  -product org.eclipse.epp.package.jee.product

command-line arguments:  -os win32 -ws win32 -arch x86 -product org.eclipse.epp.package.jee.product

!entry org.eclipse.core.resources 2 10035 2011-03-11 11:14:42.437

!message the workspace exited with unsaved changes in the previous session; refreshing workspace to recover changes.

!entry org.eclipse.osgi 4 0 2011-03-11 11:14:42.453

!message an error occurred while automatically activating bundle org.eclipse.core.resources (72).

!stack 0

org.osgi.framework.bundleexception: exception in org.eclipse.core.resources.resourcesplugin.start() of bundle org.eclipse.core.resources.

    at org.eclipse.osgi.framework.internal.core.bundlecontextimpl.startactivator(bundlecontextimpl.java:806)

    at org.eclipse.osgi.framework.internal.core.bundlecontextimpl.start(bundlecontextimpl.java:755)

    at org.eclipse.osgi.framework.internal.core.bundlehost.startworker(bundlehost.java:370)

    at org.eclipse.osgi.framework.internal.core.abstractbundle.start(abstractbundle.java:284)

    at org.eclipse.osgi.framework.util.secureaction.start(secureaction.java:417)

    at org.eclipse.osgi.internal.loader.bundleloader.setlazytrigger(bundleloader.java:265)

    at org.eclipse.core.runtime.internal.adaptor.eclipselazystarter.postfindlocalclass(eclipselazystarter.java:106)

    at org.eclipse.osgi.baseadaptor.loader.classpathmanager.findlocalclass(classpathmanager.java:453)

    at org.eclipse.osgi.internal.baseadaptor.defaultclassloader.findlocalclass(defaultclassloader.java:216)

    at org.eclipse.osgi.internal.loader.bundleloader.findlocalclass(bundleloader.java:393)

    at org.eclipse.osgi.internal.loader.singlesourcepackage.loadclass(singlesourcepackage.java:33)

    at org.eclipse.osgi.internal.loader.bundleloader.findclassinternal(bundleloader.java:466)

    at org.eclipse.osgi.internal.loader.bundleloader.findclass(bundleloader.java:422)

    at org.eclipse.osgi.internal.loader.bundleloader.findclass(bundleloader.java:410)

    at org.eclipse.osgi.internal.baseadaptor.defaultclassloader.loadclass(defaultclassloader.java:107)

    at java.lang.classloader.loadclass(classloader.java:248)

    at org.eclipse.ui.internal.ide.application.ideapplication.start(ideapplication.java:116)

    at org.eclipse.equinox.internal.app.eclipseapphandle.run(eclipseapphandle.java:196)

    at org.eclipse.core.runtime.internal.adaptor.eclipseapplauncher.runapplication(eclipseapplauncher.java:110)

    at org.eclipse.core.runtime.internal.adaptor.eclipseapplauncher.start(eclipseapplauncher.java:79)

    at org.eclipse.core.runtime.adaptor.eclipsestarter.run(eclipsestarter.java:369)

    at org.eclipse.core.runtime.adaptor.eclipsestarter.run(eclipsestarter.java:179)

    at sun.reflect.nativemethodaccessorimpl.invoke0(native method)

    at sun.reflect.nativemethodaccessorimpl.invoke(nativemethodaccessorimpl.java:39)

    at sun.reflect.delegatingmethodaccessorimpl.invoke(delegatingmethodaccessorimpl.java:25)

    at java.lang.reflect.method.invoke(method.java:597)

    at org.eclipse.equinox.launcher.main.invokeframework(main.java:619)

    at org.eclipse.equinox.launcher.main.basicrun(main.java:574)

    at org.eclipse.equinox.launcher.main.run(main.java:1407)

i solve the problem like this: 

           workspace/.metadata/.plugins/org.eclipse.core.resources/.snap

 delete .snap.

then import your project again

have a good time.