I see a couple of the exceptions below when opening an OTP file for the first time. Things seem to work anyway, but this should be investigated.

!ENTRY org.eclipse.ui.navigator 4 0 2011-04-12 21:54:34.521
!MESSAGE Cannot add main[> Erlang Model] { erl5.7.5{ kernel{ src, include}, stdlib{ src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}, xmerl{ src, include}, wx{ src, include},..}, .settings, include, src,..} to the list of segments in main[> Erlang Model] { erl5.7.5{ kernel{ src, include}, stdlib{ src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}, xmerl{ src, include}, wx{ src, include},..}, .settings, include, src,..}:: erl5.7.5[> main[> Erlang Model] ] { kernel{ src, include}, stdlib{ src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}, xmerl{ src, include}, wx{ src, include},..}:: stdlib[> erl5.7.5[> main[> Erlang Model] ] ] { src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}:: src[> stdlib[> erl5.7.5[> main[> Erlang Model] ] ] ] { zip.erl, win32reg.erl, unicode.erl, timer.erl,..}:: dict.erl[> src[> stdlib[> erl5.7.5[> main[> Erlang Model] ] ] ] ] { module, export, export, export,..}:: as a parent.
!STACK 0
org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider$CyclicPathException: Cannot add main[> Erlang Model] { erl5.7.5{ kernel{ src, include}, stdlib{ src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}, xmerl{ src, include}, wx{ src, include},..}, .settings, include, src,..} to the list of segments in main[> Erlang Model] { erl5.7.5{ kernel{ src, include}, stdlib{ src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}, xmerl{ src, include}, wx{ src, include},..}, .settings, include, src,..}:: erl5.7.5[> main[> Erlang Model] ] { kernel{ src, include}, stdlib{ src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}, xmerl{ src, include}, wx{ src, include},..}:: stdlib[> erl5.7.5[> main[> Erlang Model] ] ] { src{ zip.erl, win32reg.erl, unicode.erl, timer.erl,..}, include}:: src[> stdlib[> erl5.7.5[> main[> Erlang Model] ] ] ] { zip.erl, win32reg.erl, unicode.erl, timer.erl,..}:: dict.erl[> src[> stdlib[> erl5.7.5[> main[> Erlang Model] ] ] ] ] { module, export, export, export,..}:: as a parent.
at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider$TreePathCompiler.addParent(NavigatorContentServiceContentProvider.java:704)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.findPaths(NavigatorContentServiceContentProvider.java:769)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.findPaths(NavigatorContentServiceContentProvider.java:770)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.findPaths(NavigatorContentServiceContentProvider.java:770)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.findPaths(NavigatorContentServiceContentProvider.java:770)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.findPaths(NavigatorContentServiceContentProvider.java:770)
at org.eclipse.ui.internal.navigator.NavigatorContentServiceContentProvider.getParents(NavigatorContentServiceContentProvider.java:643)
at org.eclipse.jface.viewers.AbstractTreeViewer.getParentElement(AbstractTreeViewer.java:1643)
at org.eclipse.jface.viewers.TreeViewer.getParentElement(TreeViewer.java:606)
at org.eclipse.jface.viewers.AbstractTreeViewer.internalExpand(AbstractTreeViewer.java:1580)
at org.eclipse.jface.viewers.AbstractTreeViewer.setSelectionToWidget(AbstractTreeViewer.java:2463)
at org.eclipse.ui.navigator.CommonViewer.setSelectionToWidget(CommonViewer.java:451)
at org.eclipse.jface.viewers.StructuredViewer.setSelectionToWidget(StructuredViewer.java:1711)
at org.eclipse.jface.viewers.AbstractTreeViewer.setSelectionToWidget(AbstractTreeViewer.java:2903)
at org.eclipse.jface.viewers.StructuredViewer.setSelection(StructuredViewer.java:1667)
at org.eclipse.jface.viewers.TreeViewer.setSelection(TreeViewer.java:1124)
at org.eclipse.ui.navigator.CommonViewer.setSelection(CommonViewer.java:382)
at org.eclipse.ui.navigator.CommonNavigator.selectReveal(CommonNavigator.java:362)
at org.eclipse.ui.internal.navigator.actions.LinkEditorAction$3.run(LinkEditorAction.java:101)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.navigator.actions.LinkEditorAction$2.runInUIThread(LinkEditorAction.java:89)
at org.eclipse.ui.progress.UIJob$1.run(UIJob.java:95)
at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:134)
at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3885)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3506)
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:25)
at java.lang.reflect.Method.invoke(Method.java:592)
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)
at org.eclipse.equinox.launcher.Main.main(Main.java:1287)