When annotations are shown as colored line numbers, each time the cursor is moved from lines with one colored number to lines of a different colored number, (this could be every line depending on your history), this error dialog pops up:

Multiple problems have occurred

(!) com.vectrace.MercurialEclipse.history.GraphLogTableViewer cannot be cast to org.eclipse.ui.part.PageBookView$SelectionProvider An error has occurred. See error log for more details. An error has occurred. See error log for more details. An error has occurred. See error log for more details. com.vectrace.MercurialEclipse.history.GraphLogTableViewer cannot be cast to org.eclipse.ui.part.PageBookView$SelectionProvider

The error log shows:

Problems occurred when invoking code from plug-in: "org.eclipse.jface".

java.lang.ClassCastException: com.vectrace.MercurialEclipse.history.GraphLogTableViewer cannot be cast to org.eclipse.ui.part.PageBookView$SelectionProvider
 at org.eclipse.ui.part.PageBookView.postSelectionChanged(PageBookView.java:910)
 at org.eclipse.ui.part.PageBookView.access$3(PageBookView.java:908)
 at org.eclipse.ui.part.PageBookView$3.selectionChanged(PageBookView.java:175)
 at org.eclipse.jface.viewers.StructuredViewer$3.run(StructuredViewer.java:888)
 at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
 at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:49)
 at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
 at org.eclipse.jface.viewers.StructuredViewer.firePostSelectionChanged(StructuredViewer.java:886)
 at org.eclipse.jface.viewers.StructuredViewer.setSelection(StructuredViewer.java:1726)
 at org.eclipse.jface.viewers.TableViewer.setSelection(TableViewer.java:158)
 at org.eclipse.team.ui.history.RevisionAnnotationController.revisionSelected(RevisionAnnotationController.java:351)
 at org.eclipse.team.ui.history.RevisionAnnotationController$1.selectionChanged(RevisionAnnotationController.java:60)
 at org.eclipse.jface.internal.text.revisions.RevisionSelectionProvider.fireSelectionEvent(RevisionSelectionProvider.java:197)
 at org.eclipse.jface.internal.text.revisions.RevisionSelectionProvider.setSelectedRevision(RevisionSelectionProvider.java:185)
 at org.eclipse.jface.internal.text.revisions.RevisionSelectionProvider.access$1(RevisionSelectionProvider.java:182)
 at org.eclipse.jface.internal.text.revisions.RevisionSelectionProvider$PostSelectionListener.selectionChanged(RevisionSelectionProvider.java:59)
 at org.eclipse.jface.text.TextViewer.firePostSelectionChanged(TextViewer.java:2755)
 at org.eclipse.jface.text.TextViewer.firePostSelectionChanged(TextViewer.java:2703)
 at org.eclipse.jface.text.TextViewer$5.run(TextViewer.java:2682)
 at org.eclipse.swt.widgets.Display.runTimers(Display.java:4112)
 at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3610)
 at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1022)
 at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
 at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:916)
 at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:86)
 at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:585)
 at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
 at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:540)
 at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
 at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124)
 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:353)
 at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180)
 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:629)
 at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
 at org.eclipse.equinox.launcher.Main.run(Main.java:1438)

Session data:

eclipse.buildId=I20120608-1400
java.version=1.6.0_35
java.vendor=Apple Inc.
BootLoader constants: OS=macosx, ARCH=x86_64, WS=cocoa, NL=en_US
Framework arguments: -product org.eclipse.epp.package.java.product -product org.eclipse.epp.package.java.product -keyring /Users/ted/.eclipse_keyring -showlocation
Command-line arguments: -os macosx -ws cocoa -arch x86_64 -product org.eclipse.epp.package.java.product -data /[...SNIP...]/workspace -product org.eclipse.epp.package.java.product -keyring /Users/ted/.eclipse_keyring -showlocation

This is annoying because the error box pops up many times while browsing code, making it unusable when there are many lines that were introduced in different versions. I tried check for updates and this problem still occurs. (MercurialEclipse 1.9.1.v201111302231 mercurialeclipse.feature.group MercurialEclipse project) It seems to function if not for the dialog box. That makes it unusable with annotations turned on.