Check the "Android version to use when rendering layouts in Eclipse" and make sure you're not using a version that ends in "W" for Android Wear (e.g. API 20: Android 4.4W).
Then just change the API version to use for previewing, instead of "Automatically Pick Best", manually select the one which works for you.
If still not work for you, try to delete Android 4.4W package.
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Window > Android SDK Manager > check Android 4.4W(API 20) if it was installed > Delete package