Hi there! I know there are countless threads on this issue, but I have finally solved it.
this only applies if you have installed WPMU as an add-on domain to your hosting account, and if the member blogs are looking unstyled and not working properly (can't login to the backend, for example), BUT the main blog's permalinks are working fine.
It's directly related the how the server handles htaccess file. on install, WPMU is supposed to create its own. As an add-on domain, it's physically in a folder. The server looks up a directory, sees an htaccess file already there and uses it.
This is the problem! If this happens to you, check the main folder where WPMU is installed for your add-on domain. make sure the options is cheked to show hidden files. you're looking for one called .htaccess. note the . in front, this makes it hidden.
htaccess.dist is the one MU uses to build this file. If .htaccess is not there, make one. use the contents of htaccess.dist. Change one line, the one that reads" "Rewritebase BASE/"
take out the BASE so it says "Rewritebase /"
Check to make sure you can access the member blog backend admin area. If needed, resave the permalinks under Settings -> Permalinks. Shoudl be good to go after that.
