Why can't VS2010 open a file from network location?

I've created an FTP network location via the Add Network Location wizard. I can browse开发者_如何学Python through the folders in the File/Open dialog in VS2010, however, when I want to open a file, I get:

in VS2010:

Could not find file 'C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PageTemplate.ascx'.

in VS2008:

The system cannot locate the object specified.

Am I missing something simple or is this a known issue?