WordPress Log-in Loop

So, I was updating a blog that I manage for somebody else using one of the automatic updater plug-in deals. It some where / some how failed. Whatever. So I edit the options table, clear the active plug in list, delete the two wpau_ tables, reactive, let it clean up the install, and then finish updating. Blech.

Then I get to the last step where it opens a new window / tab to let you see if you have to upgrade the database (at which point it does when you click upgrade).

BAM! Endless WordPress log-in loop. What in the name of the Sith is going on here?

So I fiddle with it. do what that blog post says, and away we go. Why did the update fail in the first place? I also found a random PHP file that only had one line (a comment).

//Silence is golden!

Seriously? Anyway, problem fixed.