32-bit applications, including eXtyles, are not compatible with 64-bit versions of Office. You can find technical details about this limitation in the Microsoft articles, Compatibility Between the 32-bit and 64-bit Versions of Office 20103 and 64-bit Editions of Office.

Note the Microsoft recommendation:

"We recommend the 32-bit version of Office, because it is more compatible with most other applications, especially third-party add-ins."

It’s unlikely that most organizations need the additional capacity within Word that is provided by moving to the 64-bit version. When there are users within an organization who need to do CPU-intensive spreadsheet or database work, it’s actually possible to install the 64-bit versions of Excel and Access in parallel with the 32-bit versions of Word and Outlook. This approach can satisfy the needs of all users in an organization, and provide additional capabilities of products like eXtyles within your publishing team.

Not sure what version of Word you're using? Learn more here.