Error while opening an xhtml file in Mule Studio

Question

java.lang.NoClassDefFoundError: org/jboss/tools/common/text/xml/contentassist/SortingCompoundContentAssistProcessor
    at org.jboss.tools.jst.jsp.TextViewerConfigurationDelegate.getContentAssistProcessors(TextViewerConfigurationDelegate.java:24)
    at org.jboss.tools.jst.jsp.HTMLTextViewerConfiguration.getContentAssistProcessors(HTMLTextViewerConfiguration.java:112)
    at org.eclipse.wst.sse.ui.StructuredTextViewerConfiguration.getContentAssistant(StructuredTextViewerConfiguration.java:291)
    at org.eclipse.wst.html.ui.StructuredTextViewerConfigurationHTML.getContentAssistant(StructuredTextViewerConfigurationHTML.java:126)
    at org.jboss.tools.jst.jsp.jspeditor.JSPTextEditor.createSourceViewer(JSPTextEditor.java:427)
    at org.eclipse.ui.texteditor.AbstractTextEditor.createPartControl(AbstractTextEditor.java:3412)
    at org.eclipse.ui.texteditor.StatusTextEditor.createPartControl(StatusTextEditor.java:54)
    at org.eclipse.ui.texteditor.AbstractDecoratedTextEditor.createPartControl(AbstractDecoratedTextEditor.java:447)
    at org.eclipse.wst.sse.ui.StructuredTextEditor.createPartControl(StructuredTextEditor.java:1514)
    at org.jboss.tools.jst.jsp.jspeditor.JSPTextEditor.createPartControl(JSPTextEditor.java:351)
    at org.jboss.tools.jst.jsp.jspeditor.JSPMultiPageEditor$3.createPartControl(JSPMultiPageEditor.java:564)
    at org.jboss.tools.vpe.editor.VpeEditorPart.createPartControl(VpeEditorPart.java:527)
    at org.jboss.tools.jst.jsp.jspeditor.JSPMultiPageEditorPart.addPage(JSPMultiPageEditorPart.java:93)
    at org.jboss.tools.jst.jsp.jspeditor.JSPMultiPageEditor.createPagesForVPE(JSPMultiPageEditor.java:583)
    at org.jboss.tools.jst.jsp.jspeditor.JSPMultiPageEditor.createPages(JSPMultiPageEditor.java:499)
    at org.eclipse.ui.part.MultiPageEditorPart.createPartControl(MultiPageEditorPart.java:348)
    at org.eclipse.ui.internal.EditorReference.createPartHelper(EditorReference.java:670)
    at org.eclipse.ui.internal.EditorReference.createPart(EditorReference.java:465)
    at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:595)
    at org.eclipse.ui.internal.EditorReference.getEditor(EditorReference.java:289)
    at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java:2958)
    at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java:2863)