I was upgrading a WordPress MU site we work on and came across an annoying issue: core update wouldn't work the way it's supposed to. I got the following error:
Unpacking the update.
Could not copy files.
Installation Failed.
After a bit of Googling I found a thread in the WordPress forums that contained a gem of a fix:
In [...]

I've been working on one of the largest WordPress MU projects we've taken on so far the last couple of days. We've been migrating the blogo.nl blogs (a Dutch blog network started in 2005) over to WordPress MU. There were several things in this project that were nice to figure out, I'll go over two [...]

At OrangeValley, we're currently working on migrating a large Dutch blog network over from it's own proprietary system to a WordPress Multi User install, one of our more serious WordPress MU development projects. There's quite a few things about WordPress MU that I like, but what I like most is, well, that's it's WordPress :)
For [...]