I am getting the following error when i try triggering a build using the following command:
curl http://jenkins_server:port/jenkins/job/job_name/build?token=token_name>
I had the same problem after setting up a test Jenkins server. The solution was to authenticate using my Jenkins admin password:
curl -u admin: http://localhost:8080/job/Test/build?token=
Use the same username and password you use to login to Jenkins. There was no need to install additional plugins.