Trusted Locations in Excel 2013

Hi @ all, we have defined various Trusted Locations for the individual Office applications. This setting is distributed by group policy (User-Settings). The policy is correctly activated and applied to the client. When I check the Excel settings, there is a path that is grayed out and apparently not active (see attachment). It looks like this path is disabled in Excel? What surprises me, that all other paths in Excel work perfectly. Can one of you perhaps explain in principle what this grayed entry means and where the error might be under certain circumstances? Many thanks for your help... Torben