During installation, Exchange Setup modified the WebSvcExtRestrictionList metabase key. The WebSvcExtRestrictionList metabase ...

During installation, Exchange Setup modified the WebSvcExtRestrictionList metabase key.  
The WebSvcExtRestrictionList metabase key contains a list of .dll files that are either allowed or denied access to run on your server.  
Exchange setup has added and allowed the following .dll files and extension groups to run:  

           %1  
Parts of Microsoft Exchange require this modification to work properly.