Cannot use a leading .. to exit above the top directory

I've just started using visual studio 2010 to build a .net 4 website.  In my root directory I have 2 master pages, one for the main site itself, the other for an admin section.  Im building several pages to administer the site and have them in a folder underneath the root
 
website/Office/adminpage.aspx
 
whenever I try to run this page, I get this error
 
Cannot use a leading .. to exit above the top directory
 
If I create the admin page without using the master page, it works ok.  Ive tried commenting out the references to the css files on the master page, but it makes no difference.  Ive done exactly the same thing in previous .net 3.5 projects without any problems.  Anyone have any idea whats going on here ?
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