Hello Horacio,
At this point we are missing what outlook version you have and what exact version of Unity or UConnection.
1-Check Compatibility Matrix: Cisco Unity and the Software on Subscriber Workstations
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/compatibility/matrix/cuclientmtx.html#wp364674
and see if everything matches accordingly to the supported versions, this is a well known issue. If everything does continue with option below.
2-Beside the server name try with the IP instead.
3-Check if you have turned on the SSl, if you do turn it off and try again
Best Regards,
David Peck