ERROR: Build failed with: exit status 1

On several runners i'm getting this kind of problem:

DEBU[0018] 6a22da4b 499 Build log updater finished.     
DEBU[0018] 6a22da4b 499 Build log:  gitlab-ci-multi-runner 0.5.0 (c38415a)
Using Shell executor...
Running on Emil-MacBook-Pro.local...

Fetching changes...

ERROR: Build failed with: exit status 1

How to debug this kind of problems?

I was following this installation guid: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/blob/master/docs/install/osx.md