Files not found when opening them

I'm using Dreamweaver CS3. Every time I try and open an existing page from
either inside the site window or from the Finder (I'm a Mac user) nothing
happens. If I try and go via 'open recent files' or use the 'open with' command
in the Finder, I get the same error message saying the file 'was not found'. I
can preview by opening the file from inside my browser but it seems Dreamweaver
can't recognise that the files are where it says they are.

I have Dreamweaver CS3 installed on two machines and I have the same problem
on both computers. Can anybody tell me what's going on? Cheers! This is kind of
urgent so if you can help me soon I'd be very pleased!