WordPress MU

Hello
all at once i cannot see any images for any blogs.
for example
blogs/music-blog/files/2007/10/DSC2444.jpg
I get a 404. But I've checked in blog.dir and it exists
So could help me understanding what happened , where i have to look. (htaccess, wp_xx_options ,....??)
thanks a lot
pls is urgent

I've found it, the blogs.dir user was root instead apache, just made a chown and they reappeared
thanks