Removing a persistent build error

I got my first build error yesterday after using Middleman for months. Here’s the sequence of events.

  1. Unwittingly put a random directory in my project.
  2. Committed changes
  3. Tried to build, got an error.
  4. Discovered random directory and removed it, then committed change.
  5. Tried to build again.
  6. Build was successful, but I get an error that it can’t find a file from that erroneous directory.

So how do I clean that up so that I don’t get the build error anymore?