A number of forum posts popped up over the last week+ with issues running the system cron job. The cron would report the user/password is incorrect and unable to authenticate, even though the credentials were correct. The issues started to arise around the time v4.4.4 was released so most people thought it was due to changes in that release.
The issue is actually caused by changes to the password hashing mechanism, and consequently the authentication method, in Joomla, starting in vJ3.2.1 and J2.5.18. Those versions require changes to how extensions like CiviCRM verify authentication credentials.
The fix for those versions will be included in CiviCRM v4.4.5 (http://issues.civicrm.org/jira/browse/CRM-14208). In the meantime, you can apply the following patch to fix your existing installation: https://github.com/civicrm/civicrm-core/pull/2512/files
If you have not yet upgraded to those Joomla versions, please be aware that you will need to patch your CiviCRM installation when you do so in order to retain the ability to run scheduled jobs through the cron. Or you can wait until v4.4.5 is released and upgrade both Joomla and CiviCRM concurrently.