Homebrew errors; update fails
The brew doctor should be helpful about this, next best thing to try is repairing formulae from taps with brew tap --repair. If that still does not help, try the following steps:

brew untap &lt;X&gt; where  is from brew tap.

cd $(brew --prefix)

git clean -fd

git reset origin/master --force

brew update

brew tap &lt;X&gt; to have your taps again.