Wich version of ocs have you installed on your server?
error 400 means that server ocs version is lower than agent version. In this case, it does not running correctly.
Which is correct is : server 2.1.2 agent 2.1.1/2.1.0/2.0.x/1.x
Which is uncorrect: server 2.1 agent 2.1.1/2.1.2 or server 2.0.x agent 2.1.x