eXtyles does not support the 64-bit version of Microsoft Office.
Determine whether you’re running the 32-bit version or the 64-bit version of Microsoft Office by clicking Help on the File tab of the Word ribbon. On the right-hand side, you should see “About Microsoft Word” and something like “Version: 14.0.6123.5001 (32-bit).”
eXtyles (along with many other third-party add-ons) is not compatible with the 64-bit version of Office, although it is compatible with the 64-bit version of Windows. See Microsoft’s bulletin at http://technet.microsoft.com/en-us/library/ee681792.aspx.
You must have full administrator privileges for the C:\Program Files (or C:\Program Files (x86)) directory.
Once you’ve confirmed that you’re running 32-bit Office and have full administrator privileges, uninstall eXtyles via the Windows Control Panel and reinstall eXtyles.