software center "donwload" button doesn't work with any app

[Andres Molina]

In Ubuntu 12.04 LTS, software center doesn't let me "click" or press the "download" button at any app. I've unistalled and istalled again the software center, but the problem goes on.
Here it is:
2013-04-07 15:06:38,925 - softwarecenter.ui.gtk3.app - INFO - setting up proxy 'None'
2013-04-07 15:06:38,941 - softwarecenter.db.database - INFO - open() database: path=None use_axi=True use_agent=True
2013-04-07 15:06:40,685 - softwarecenter.backend.reviews - WARNING - Could not get usefulness from server, no username in config file
2013-04-07 15:06:41,713 - softwarecenter.ui.gtk3.app - INFO - show_available_packages: search_text is '', app is None.
2013-04-07 15:06:43,664 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open()
2013-04-07 15:06:56,674 - softwarecenter.db.update - INFO - skipping region restricted app: 'Comentarios Web' (not whitelisted)
2013-04-07 15:07:00,887 - softwarecenter.db.update - INFO - skipping region restricted app: 'Bulleti d'esquerra de Calonge i Sant Antoni ' (not whitelisted)
2013-04-07 15:07:06,879 - softwarecenter.ui.gtk3.app - INFO - software-center-agent finished with status 0
2013-04-07 15:07:06,881 - softwarecenter.db.database - INFO - reopen() database
2013-04-07 15:07:06,882 - softwarecenter.db.database - INFO - open() database: path=None use_axi=True use_agent=True

Besides, it says:

No se ha podido localizar el paquete pkgname