I finally solved this error after spending all day on it….
wordpress mu “ERROR: WordPress requires Cookies but your browser does not support them or they are blocked.” – Google Search
The solution, that I haven’t seen posted anywhere, lies in how you specified the domain name when installing WPMU. I specified simply “blogs” when I should have used “blogs.domain.com”. This caused the cookie to be created with “blog.local” and IE and Firefox did not accept that.
Thank God for Opera which accepted it and let me view the cookie.