After trying everything on the books (http://blogs.technet.com/b/nishants/archive/2010/08/23/troubleshooting-user-profile-sync-issues-in-office-sharepoint-server-2007.aspx) I wasnt able to solve it, including with the stsadm commands:
stsadm -o sync -ignoreisactive 1
stsadm -o sync -deleteolddatabases 0
stsadm -o sync
Then, after browsing the ULS I found the following error:
User Profile Import: Error while querying for whether the import is in progress:
System.Net.WebException: The underlying connection was closed:
An unexpected error occurred on a send. ---> System.IO.IOException: Authentication failed because the remote party has closed the transport stream.