Search and Category Issues…

On my website, that I’m hoping to launch with some friends on March 1st, if you click on categories you get the error message saying the information was not found, same thing if you search. The post titles come back, but when you click on the post it doesn’t show up. Another error message saying the post was not found.
All the post show up on the front page/main page of the blog, but no where else.
We are using the most up to date version of wp-mu if that helps any body. Also sorry if this has been posted twice. My account said it hadn’t been posted and I couldn’t find it on the topics list. i don’t know what happened.