Biblatex is a fantastic bibliography/citation manager for LaTeX. It trumps the older bibtex for its much easier customizability and configuration. It does however, have one bug that can be very perplexing to figure out due to the misleading error message that results: "Could not find all biber source files". At first glance this message seemed straightforward enough to send me poking about the project file structure and build system, checking paths and names. When all that seemed intact, I started trying building the document from different locations. Then I checked out older version-controlled revisions of the project that I was sure I had built successfully, and when these, too, failed, I started to look at my TeX installation. And so on and so on, and before I knew it ... poof! there went most of my morning.

This was all a wild goose chase, though, and luckily I came across this discussion before I got too far. (Well, at further too far, at any rate.) Turns out that this is a known bug with the Biblatex engine, "biber". The fix is to clear the "biber" cache. You can locate the "biber" cache by running:

$ biber --cache

and then you can "rm -rf" it with extreme glee or just do it all in one step with:

$ rm -rf $(biber --cache)