Revit Architecture 2011 Error Message

Hi,
When I attempted to open Revit Architecture 2011 an error message showed up. Actually, it showed up before Revit even started.
Please suggest a fix for this error as soon as possible. The error message is given below.
Thank you in advance.

System.ArgumentExcepton: A standard item with the Id [Measure_Split_Button] already exists in the collection!
in
Autodesk.Windows.TooIBarsQuickAccessToolBarSource.OnCanInsertitem(Object sender ValidateltemEventArgs e)
in SystemEventHandler1 .invoke(Object sender TEventArgs e) in Autodesk.Wandows.ToolBatsval.datingRibbonltemCollection.InsettltemUnt32
index. Ribbonitem item)
in System.Colledions.ObjedModeLCollectio&1 .Add(T item) in
Autodesk.Windows.ToolBars.QuickAccessTool8ar5outce.AddStandardftem(Ribbo
nItem item)
in UlFramework.RevitQueckAccessToolbar.AddStandardBunonsO in UlFramework.RevitRibbonControlioadRibbonCoritrol(RevitRibbonControl ribbonControl. String strXamlFile)
in ARibbonControlwrapperIoadStaticTabsForProduct(ARibbonControlWrapper
OK
