Active Checks how to

[Keitamax]

Hi all,
first I'm a beginner with Zabbix so excuse me if I say/ask obvious stuff. My english may be weird, sorry for that too...

I work with a Zabbix 1.8.4 virtual appliance.
I am trying to set up active checks with a Windows agent host, but I get the following error in the agent log file:

Get active checks error: *** Cannot connect to [10.33.171.18]:10051 [Une tentative de connexion a échoué car le parti connecté n'a pas répondu convenablement au-delà d'une certaine durée ou une connexion établie a échoué car l'hôte de connexion n'a pas répondu.] 
(translation : Connexion failed because the connected side didn't answer properly beyon a certain duration or an established connexion failed because the connection host didn't answer)
2864:20110629:170614.593 In process_active_checks('10.33.171.18',10051)
2864:20110629:170614.593 End of process_active_checks()

The following line also sometimes appears :

2864:20110629:172045.156 refresh_active_checks('10.33.171.18',10051)

Here is a part of my zabbix_agentd.conf:

Server=10.33.171.18
Hostname=PCTest2

In the web UI, I named my host 'PCTest2', since the names must be the same for the active checks to work.
I tried passive checks, they work just fine. I guess I'm missing something in the configuration for active checks...

Would anyone be able to help me?

[Keitamax]

I read the server log file (with debugmode = 4), and no error is reported. Help please!!!

[Keitamax]

I really need to make it work, isn't there anybody to help me?