Emails inside process always staying in state Created

Emails inside process always staying in state Created

  
Ok, here's my scenario.
I have a really basic process:
Starts on creating and entity
Sends an e-mail
Has Human Activity
Ends
 
My problem is that each process created hangs on the Send Email activity. When consulting the Service Center logs I've learnt that all sent email activities are in state created and stays in that way like... forever (Ok, just hit this problem 2 days ago, so my forever is as long as that period).
I can send E-mail inside a screen action so I'm guessing that my server and e-mail configuration is OK. I'm retrieving all the variables sent to my process's activities from the DB using Actions.

I have tried to look everywhere else I could imagine and still don't understand what am I doing wrong. I'am using the latest version of service studio (6.0.1.7).
Is there any blessed soul that can help me with this? I lost all my imagination I still can get what could be wrong with my application. :)

Many thanks in advance