Exchange server problem: I cant send emails from a particular computer

I am having troubles sending emails with a particular computer.

I have tried from Outlook Web Access, after writing the email i hit the send button. Then shows me a message that says “Sending…”, after a while shows me the following error “Microsoft Exchange issued an unexpected response (12031)”, and does not send the mail. If i go to the light Outlook webacces, i can send the emails without any trouble.

Ok then, i tried to configure outlook to receive exchange mail, everything looks normal, i receive all my mails, but when i try to send any mail, it keeps telling me that outlook is not connected and needs to have connection and is not sending anything.

Any help would be appreciated for both cases, OWA and normal Outlook.