I tried to redirect my non-www. URL and now I have problems

I attempted to redirect my non-www. version of my site to the www. URL and now I seem to be having problems. I noticed that my hosting company only has the non-www URL listed in the “domain management”, but everything I have been linking, posting, etc. is the www. URL. When I tried to do a redirect so that one points to the other, things went bad. So I changed it back so that both work.

I have been told that one needs to redirect to the other so that I will avoid having search engines flag me for duplicate content. My problem now is that anytime I go to do an update or make a change it asks me to log in again. Unfortunately it is not recognizing my user name and password when I do this. It doesn’t say login has failed, it just appears to refresh and doesn’t accept what I know to be a correct user name and password…

Any ideas on how to fix this? Thanks.