Tools | DB2 Command Window menu option error: "Item has already been added. Key in dictionary: 'd (4302197)

When I go to Tools  | DB2 Command Window menu option, I get the error:

Exception: System.ArgumentException
Message : Item has already been added. Key in dictionary: 'db2codepage' Key being added: 'db2codepage'
Stack Trace:
at System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add)
at System.Collections.Hashtable.Add(Object key, Object value)
at System.Collections.Specialized.StringDictionary.Add(String key, String value)
at Quest.Toad.DB2.LaunchEXE.Run(String exeName, String argsLine, Int32 timeoutMilliSeconds)
at Quest.Toad.DB2.DB2CommandWindow.OpenDB2CommandWindow()