The problem may be caused by a rogue 3rd-party Office addin that's installed on your computer. Try starting Word, for example, in safe mode (i.e. hold down the Ctrl key while starting Word). If the problem goes away in safe mode, a rogue 3rd-party Office addin is the most likely cause. Re-start Word and disable all 3rd-party Office addins, then re-enable them one at a time, re-starting Word each time till you find the culprit - which you can either uninstall or look for an update.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]