Before starting your controller agent make sure that in the folder C:\Users\<username>\AppData\Roaming\Neotys\NeoLoad\v6.10 you do not have a controller-agent.lock file that is still there. If it's the case remove it and try again to start your agent. This lock file should only be there when a controller agent is running.
If it does not work then look at the log files in C:\Users\<username>\AppData\Roaming\Neotys\NeoLoad\v6.10\logs and especially the files controller-agent*** for more information.