Bug 117925 [Intro] Misleading exception message in WelcomeEditor.init()
... it says it expects an IFileEditorInput, but it actually checks for WelcomeEditorInput. Suggested patch appended.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/dialogs/WelcomeEditor.java
return;
                        }
                    }
                    if (previousTabAbortTraversal) {
                        previousTabAbortTraversal = false;
                        return;
                    }
                    
                    
                    StyleRange previousLink = findPreviousLink(text);
                    if (previousLink == null) {
                        if (text.getSelection().x == 0) {
                            
                            StyledText previousText = previousText(text);
                            previousText.setSelection(previousText
                                    .getCharCount());
                            previousLink = findPreviousLink(previousText);
                            if (previousLink == null)
                                focusOn(previousText, 0);
                            else {
                                focusOn(previousText, previousText
                                        .getSelection().x);
                                previousText
                                        .setSelectionRange(previousLink.start,
                                                previousLink.length);
                            }
                        } else {
                            
                            focusOn(text, 0);
                        }