With Karaf 3.0 we introduced the role based authentication for commands and JMX. So you likely didn't log into Karaf using any credentials. If you want to use a "restricted" command like stoping starting a bundle you either have to log-in using the right credentials, or need to disable the authentication for this command. To do so edit the etc/org.apache.karaf.commands.acl.bundle.cfg configuration.
start[/.*[-][f].*/] = admin
start = manager
stop[/.*[-][f].*/] = admin
stop = manager
Right now the default behavior is to have admin rights for start -f (force) where start is open to any "manager". So you have to change the start/stop command to be available for manager also.