Well, I'm stumped.

I have two identical servers both running Debian.
On one server the update goes just fine on all the domains and forums. On the other I get the "Packages directory or one of the files in it are not writable" error.
I promise you, ALL the files and directories and *everything* in that directory are writable.
I've created a "temp" dir and set permissions and owner on it, but I cannot get past this message no matter what I do.
Any ideas? I'm pulling my hair out over this.