Tmux environment crashing


A couple of weeks ago I setup my local dev environment with Thoughtbot’s Laptop script.
However when I’m developing in a Tmux session, my environment regularly crashes with this error:

/usr/local/Cellar/rbenv/1.0.0/libexec/rbenv-commands: fork: Resource temporarily unavailable

Then I have to close my Tmux session and start a new session with ‘tat’

does any one have experience with this issue?

thanks for your help,