WordPress MU

Hi all.
My mu installation was running since a long time. And Everything was working right.
The problem is that i modified my .htaccess 2 days ago.

And now, my home page is working as usually, but when i try to go on page or a post, nothings work.

I got a 404 error with this message:

'The requested URL /my-page-or-post/ was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.'

I don't know what to do...
Anyone can help me please ?
The url of my site is: http://kune.fr and http://musique.kune.fr is a blog running here.

Solved.
I explain what i did:

The problem is that i modified my htaccess and removed it.

To solve that, i removed it from my server (i didn't saw it so i used command line), edit the htaccess.dist (on the second line RewriteBase Base/ to RewriteBase /
Saved it as .htaccess and upload
All goes right...

Gracias MAT_, esto ha resuelto tambien mi problema...

Thanks MAT!