Gui enables run when the assembly specified on the command line is not found

[MichiGreat]

Belongs to: NUnit 2.5.10

If you start nunit for example like this:
nunit.exe /run x:\doesnt_exists
and then click the "Run" button (which is enabled after the error message that states that the file could not be loaded), an exception is thrown:

System.NullReferenceException: Der Objektverweis wurde nicht auf eine Objektinstanz festgelegt.
bei NUnit.Util.TestLoader.RunTests(ITestFilter filter)

It seems that the error is in file TestLoader.cs in line 618: Perhaps Services or Services.UserSettings is null. All other calls in RunTests(ITestFilter) don't look suspicious to me to raise that exception or would cause to happen the exception in a different place (like if filter was null - exception would be thrown somewhere in BeginRun or afterwards).

Full strack trace:

System.NullReferenceException: Der Objektverweis wurde nicht auf eine Objektinstanz festgelegt.
bei NUnit.Util.TestLoader.RunTests(ITestFilter filter)
bei NUnit.UiKit.TestSuiteTreeView.RunTests(ITest[] tests, Boolean ignoreCategories)
bei NUnit.UiKit.TestSuiteTreeView.RunSelectedTests()
bei NUnit.UiKit.TestTree.RunSelectedTests()
bei NUnit.Gui.NUnitForm.runButton_Click(Object sender, EventArgs e)
bei System.Windows.Forms.Control.OnClick(EventArgs e)
bei System.Windows.Forms.Button.OnClick(EventArgs e)
bei System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
bei System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
bei System.Windows.Forms.Control.WndProc(Message& m)
bei System.Windows.Forms.ButtonBase.WndProc(Message& m)
bei System.Windows.Forms.Button.WndProc(Message& m)
bei System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
bei System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
bei System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

[Charlie Poole (charlie.poole)]

Strangely, I get the error but with a different stacktrace. In addition, the menu items Run All and Run Selected are also enabled and (naturally) cause a failure as well. This occurs with or without the user of the /run option. I'm changing the description, since the main problem is that these UI elements should not be enabled at all.