vCO 5.5.1 - Cannot login : user unknown

Hello, I'm in the process of deploying vCO appliance 5.5.1 and I'm going crazy about this problem : when I test a login on the vCO configuration page, it works but in the client (Java applet or installed client) I get a "invalid password/username" and "user unknown" in the logs.

I've tried both SSO and LDAP authentication with the same result.

I tried many tricks found on the VMware forums like : vCO 5.5.1 - user unknown - Unable to log in to Orchestrator Client using SSO - Can't login - Can not login to the Orchestrator Client but none of these worked.

Any help would be greatly appreciated

Thank you !