user settings css does not load... why?

I have a test site with a strange condition... everything woseems to work fine apart from the User Settings link... it loads basic data and no css... better than a WSOD, but I still can't fix it.

Running 1.7.1 upgraded from 1.6.2, I switched off all the plugins, re-uploaded the core settings folder and contents and the standard Mod directory... no differance at all... still broken.  Can anyone help me please??