Configure Tentacle Deployment agent

Hy,
I have this message when I configure a Tentacle Deployment agent and when I vérify credentials :

Connected successfully, Octopus Server version: 2.5.7.384
Authenticating as administrator…
Error:

Octopus.Client.Exceptions.OctopusServerException:

at Octopus.Client.OctopusClient.DispatchRequest[TResponseResource](OctopusRequest request, Boolean readResponse) in y:\work\refs\heads\master\source\Octopus.Client\OctopusClient.cs:line 428
at Octopus.Client.OctopusRepository.UserRepository.SignIn(LoginCommand loginCommand) in y:\work\refs\heads\master\source\Octopus.Client\OctopusRepository.cs:line 849
at Octopus.Tools.TentacleConfiguration.SetupWizard.TentacleSetupWizardModel.VerifyCredentials(ILog logger) in y:\work\refs\heads\master\source\Octopus.Tools\TentacleConfiguration\SetupWizard\TentacleSetupWizardModel.cs:line 271

Can you help me ?

Hi Matthias,

Thanks for getting in touch! Really sorry about the delay in getting back to you.
When you setup a tentacle in polling mode, it is looking for an Octopus User account to connect to to setup its credentials within Octopus.
Could the Octopus server have been offline or not had its port configured through the firewall? Or could that tentacle have blocked any outside communication?

Vanessa