Error message: Problem Converting OMML to MathML

OMML is an acronym for Microsoft's Office Math Markup Language, the language Microsoft Office uses to encode equations. The OMML equation editor is the one introduced in Word 2007, and continues in subsequent versions on Windows and Mac.

You're working in Word, and some or all of the equations in the document were created with Word's OMML equation editor. You want to convert all the OMML equations to MathType equations, and are using MathType's Convert Equations command (on the MathType tab in Word) to do so. Almost immediately after clicking Convert, you see this error message:

Clicking Yes leads you to this page for further instructions, and may be why you're here now. Clicking No stops the conversion process, and no OMML equations are converted.

The simple condition to trigger this error message is for the file not to be present on your computer. More generically, it's possible for the file to be present, but if it's not in the location where MathType expects to find it, you will get the error.

1. First, verify whether the file is present or not. Where the file is located depends on your version of Office and your version of Windows, and whether one or both of them are 64-bit:
   • Word 2007: C:\Program Files\Microsoft Office\Office12
   • Word 2010: C:\Program Files\Microsoft Office\Office14
   • Word 2013: C:\Program Files\Microsoft Office 15\root\office15
   • Word 2016: C:\Program Files\Microsoft Office\root\Office16
   • If the folder identified for your version of Word is not present, check the same path in C:\Program Files (x86).
2. If the file omml2mml.xsl is present, create a folder as described below, and copy the file to the new folder. For example…
   • If you're using Word 2016, and the file is present here, C:\Program Files\Microsoft Office\root\Office16, create this folder structure if it does not exist: C:\Program Files (x86)\Microsoft Office\root\Office16. (Note there is no space in Office16.) Copy the file omml2mml.xsl to this new folder.
   • If you're using Word 2013 or earlier, adapt the instructions accordingly, based on the paths shown in step 1.
3. If the file omml2mml.xsl is not present, download it here, unzip the file, and follow the instructions shown in step 2.

We hope this has been helpful. As always, please let us know if you have questions about this, or if you have additional techniques that work. We'd love to hear from you.