You have typed one of the characters ($ \ ^ _) that begins a string of TeX commands. After you have finished typing the commands, ...

You have typed one of the characters ($ \ ^ _) that begins a string of TeX commands. After you have finished typing the commands, hit Enter to convert them into normal MathType expressions. If you want to enter one of these special characters, just type it twice or turn off this feature using the Workspace Preferences command on the Preferences menu.
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