Frontpage Extensions needs to be enabled for your website hosting account if you are using Microsoft Frontpage to develop your website. These extensions can occasionally become corrupted especially when there is excessive publishing to the hosting account, generally a remove and reinstall of Frontpage Extensions helps resolving the problem.
To (re)install Frontpage Extensions:
Click Setup Frontpage Extensions in domain hosting account control panel.
Click Install / Reinstall Extensions button, there is a enabled/disabled status shown on the page after the process.