Dear Pablo,
This is a widely discussed topic which tends to be asked a lot in the forum and there even is an
offical guide to complete the installation (which often is the solution, not your case though), take a look to
this or
even this topic to see similar discussions.
If I had to pinpoint anything, I would blame the svn client installation and/or configuration (did SVN tortoise installed properly? do you have access to svn command line interface? are you behind a proxy or somehow restrited network?)
Regards,
José Díaz.