The error will show up when
1. Authentication is not enabled in Prolaborate for an Enterprise Architect model which has Security enabled or
2. the Authentication details entered are incorrect.
If you are getting this error even when Security is not enabled for this model, Security might be enabled at the Active Directory level. You need to create a user from Enterprise Architect and use that credentials for Authentication in Prolaborate.
If you are getting this error even after giving the right credentials, check if you are able to login to the model using Enterprise Architect.
If no, the credentials are invalid.
If yes, you must be using the default credentials when you enabled Security in EA, which is admin and password. You need to use the Change Password option once to resolve the issue. Change the password in EA and use the same in Prolaborate. You can even change the password to password. Once you go back to Prolaborate and refresh the Repositories page, the status will change to Active.