The MathType toolbar used to be attached to the main MathType window, but now is floating and won't re-dock and attach to the main window:
Reason
It's easy to undock the toolbar without realizing it. The toolbar should re-dock by double-clicking its title bar (identified by the word "Equation" above), but it doesn't. This will be addressed in MathType 7.
Solution
To re-dock the toolbar, use the shortcut Ctrl+Alt+D.
Naschrift
Je kunt ook dubbelklikken op de toolbar... dat werkt ook...:-)