Moved to Design & Development Software

I don't personally use DW, but do the files you're trying to open have either a .htm(l), .css, .js, .php or .asp extension?

i.e. if it's not a file unique to Dreamweaver, but a web-related file, then there's either an issue with your CS3 or an issue with the file permissions.

What *exactly* does the error say?

(If it is a DW-specific file, ignore everything I just said!)