Jin Lee,
What version of ArcGIS Server are you running? I suspect ArcGIS Server .NET v 9.3.1 with IIS.
I believe you've encountered a bug. The problem is you have a folder name that begins with a number. This causes the server to return some invalid information, and thus, arcgis.com can't connect to your server. You can either upgrade your server to the latest version, or simply try renaming your folder named 2005 so that it begins with a letter.
Thanks,
Mike