Access with IE a HTML-File on a Networkdrive(system context)

I want access an html-file with internet explorer 7 on a vista client. This
html file is situated on a network share, which was connected at system
context.

I get an error, that the ie7 couldn't access this location, but i can open
this file with notepad.

I have read something about integrity levels. My ie7 runs at level high,
because uac is deactivated on this client.

Have anybody an idea, what i can make to get it work?

Best regards

Matthias Kracht