When I open a pom.xml file in STS 2.2.1, it throws an error. Anybody seen or worked around this?

Code:
eclipse.buildId=M20090917-0800
java.fullversion=J2RE 1.6.0 IBM J9 2.4 Windows XP x86-32 jvmwi3260sr5ifx-20090821_41076 (JIT enabled, AOT enabled)
J9VM - 20090821_041076_lHdSMr
JIT  - r9_20090518_2017
GC   - 20090417_AA
BootLoader constants: OS=win32, ARCH=x86, WS=win32, NL=en_US
Framework arguments:  -product com.springsource.sts.ide
Command-line arguments:  -os win32 -ws win32 -arch x86 -product com.springsource.sts.ide


Error
Tue Nov 24 06:42:53 EST 2009
Problems occurred when invoking code from plug-in: "org.eclipse.contribution.xref.core".

java.lang.NoClassDefFoundError: org/springframework/ide/eclipse/aop/core/Activator
	at org.springframework.ide.eclipse.ajdt.ui.xref.AopReferenceModelReferenceProvider.getXReferences(AopReferenceModelReferenceProvider.java:124)
	at org.eclipse.contribution.xref.core.XReferenceAdapter.getXReferences_aroundBody8(XReferenceAdapter.java:80)
	at org.eclipse.contribution.xref.core.XReferenceAdapter$AjcClosure9.run(XReferenceAdapter.java:1)
	at org.eclipse.contribution.xref.core.IXReferenceProvider$SafeExecution.ajc$around$org_eclipse_contribution_xref_core_IXReferenceProvider$SafeExecution$1$b538bdbdproceed(IXReferenceProvider.aj:1)
	at org.eclipse.contribution.xref.core.IXReferenceProvider$SafeExecution$1.run(IXReferenceProvider.aj:136)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
	at org.eclipse.contribution.xref.core.IXReferenceProvider$SafeExecution.ajc$around$org_eclipse_contribution_xref_core_IXReferenceProvider$SafeExecution$1$b538bdbd(IXReferenceProvider.aj:142)
	at org.eclipse.contribution.xref.core.XReferenceAdapter.getXReferences(XReferenceAdapter.java:80)
	at org.eclipse.contribution.xref.internal.ui.providers.XReferenceContentProvider.createXRefTree(XReferenceContentProvider.java:114)
	at org.eclipse.contribution.xref.internal.ui.providers.XReferenceContentProvider.initialize(XReferenceContentProvider.java:99)
	at org.eclipse.contribution.xref.internal.ui.providers.XReferenceContentProvider.inputChanged(XReferenceContentProvider.java:43)
	at org.eclipse.jface.viewers.ContentViewer.setInput(ContentViewer.java:270)
	at org.eclipse.jface.viewers.StructuredViewer.setInput(StructuredViewer.java:1634)
	at org.eclipse.contribution.xref.ui.views.XReferenceView.selectionChanged(XReferenceView.java:196)
	at org.eclipse.ui.internal.AbstractSelectionService.firePostSelection(AbstractSelectionService.java:179)
	at org.eclipse.ui.internal.AbstractSelectionService$2.selectionChanged(AbstractSelectionService.java:71)
	at org.eclipse.jface.text.TextViewer.firePostSelectionChanged(TextViewer.java:2731)
	at org.eclipse.jface.text.TextViewer.firePostSelectionChanged(TextViewer.java:2679)
	at org.eclipse.jface.text.TextViewer$5.run(TextViewer.java:2658)
	at org.eclipse.swt.widgets.Display.runTimer(Display.java:3943)
	at org.eclipse.swt.widgets.Display.messageProc(Display.java:3135)
	at org.eclipse.swt.internal.win32.OS.DispatchMessageW(Native Method)
	at org.eclipse.swt.internal.win32.OS.DispatchMessage(OS.java:2410)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3471)
	at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
	at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
	at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
	at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)
	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:368)
	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:37)
	at java.lang.reflect.Method.invoke(Method.java:599)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:559)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1311)