Why do I receive an "Unknown error" when browsing SharePoint site in Office Mobile?

Browsing a customized SharePoint site in Office Mobile (Document Connection) sometimes results in Unknown error fffffffc00ce558.

SharePoint sites can be customized and these customizations can sometimes impact the ability for Office Mobile to browse the site. The site can be browsed by entering the URL into the phone's web browser. However, the content for such a site will not be available in Office Mobile.