This problem can occur when authors insert equations with the Equation Builder feature in Word 2007 or 2010, but you’re using Word 2003 for editorial. The Word 2007/2010 equations are not backward compatible with Word 2003. Whenever you get a DOCX file:

• Open the file with Word 2007/2010.
• Run eXtyles Font Audit. Font Audit will add this message, “This document has equations created with the Microsoft Office 2007 Equation Builder” to the alert if there are any problematic equations.
• If this message doesn’t appear, then you can just process the file as you normally do. However, if it does appear, use MathType 6.8 to convert all of the Word 2010 equations to MathType.
• Proof the equations—the conversion is good, but it’s not bullet-proof. You may need to complete some manual cleanup of the equations in MathType.

At this point you can move the file into your regular workflow.