In Visual Studio 2010 Under certain circumstances the you may encounter problems opening the Test View window. (see image below)

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Luckily it is easy to fix.  To make it go away, you need to close/reopen Visual Studio.

If you don’t want this ever happening again, do the following:

1. Go to the Tools main menu -> Options… | Test Tools

2. Check the checkbox “Show all settings” to see the Test Tools settings

3. For the condition that reads “ When changes are made to the tests and background discovery of test methods is not enabled” (#9 from the top), choose “Don’t prompt”

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Error Text Below: 
An exception was encountered while constructing the content of this frame. This information is also logged by running the application with the 7
log parameter on the command line, which stores results in “C:\Users\Bob\AppData\Roaming\Microsoft\VisualStudioUO.O\ActivityLog.xml’.
Exception details:
System.Reflection.TargetlnvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentException: There
is already a command handler for the menu command b85579aa-8be0-4c4f-a850-90902b317571 : 13074.
at System.ComponentModel.Design.MenuCommandService.AddCommand(MenuCommand command)
at Microsoft.VisualStudio.TestTools.Vsip.CommandHelper.AddCommand(JMenuCommandService menuService, EventHandler invokeHandler,
EventHandler statusHandler, CommandiD id)
at Microsoft.VisualStudio.TestTools.TestCaseManagement.TestViewToolWindowJnitializeo
at Microsoft.VisualStudio.TestTools.TestCaseManagement.TestViewToolWindowHost..ctorO
--- End of inner exception stack trace ---