Umbraco version: 4.7.1  / .NET 4 / Windows 7 / IIS 7

Hi

I recently installed Umbraco 4.7.1 - all was working fine with the Rich text editor, but now I'm receiving the following error:

Item has already been added. Key in dictionary: 'undo'  Key being added: 'undo'Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.ArgumentException: Item has already been added. Key in dictionary: 'undo'  Key being added: 'undo'

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 

[ArgumentException: Item has already been added. Key in dictionary: 'undo'  Key being added: 'undo']
   System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add) +9360699
   System.Collections.Hashtable.Add(Object key, Object value) +11
   umbraco.editorControls.tinymce.tinyMCEConfiguration.init() +1141
   umbraco.editorControls.tinymce.tinyMCEConfiguration.get_SortedCommands() +21
   umbraco.editorControls.tinymce.tinyMCEPreValueConfigurator.OnLoad(EventArgs e) +1615
   System.Web.UI.Control.LoadRecursive() +74
   System.Web.UI.Control.LoadRecursive() +146
   System.Web.UI.Control.LoadRecursive() +146
   System.Web.UI.Control.LoadRecursive() +146
   System.Web.UI.Control.LoadRecursive() +146
   System.Web.UI.Control.LoadRecursive() +146
   System.Web.UI.Control.LoadRecursive() +146
   System.Web.UI.Control.LoadRecursive() +146
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

This occurs when:

1) Viewing or editing a page that has a Richtext Field data type in its Document Type (Content mode)

2) Clicking on the Richtext Field data type in Developer mode. 

I have tried restarting the app pool & IIS, but the error remains. 

One thing I did was change the names of a couple of document types and master templates. But even changing these back to what they were doesn't fix the problem.

The tinyMceConfig.config file is as per the install.

Any thoughts?

Thanks in advance