I had this problem, too. ([url=http://forums.b2evolution.net/viewtopic.php?t=3786]Check this thread[/url].) I had to edit the umask setting on my server. That's what was making uploaded files have permissions of 600.

The 'umask setting on my server' ??
Now you are talking chinese to me.

Do you mean, my hosting provider had changed somothing on the server ?
And I have to ask them to do 'something' ?
Or is it something I can do in my cpanel ?

I'm not sure. Here's the [url=http://us2.php.net/umask]php page for umask()[/url]. It's something that can be done is a script, but I think your server also has a default setting. I would ask them what it is and see how they suggest you change it.

In /admin/b2upload.php there are always to lines where chmod() gets used to set the perms to 644.

But they have been commented out before the Dawn release.

The solution would be to just remove those comment chars (lines 118, 123, 155 and 160).