For some reason, it seems very hard to upgrade from Joomla 1.6.3 / 1.7 to 2.5.
In order to upgrade successfully, I manually upload the relevant Joomla package into the /tmp directory of the site and install 'from url' in the Extensions Manager of Joomla.
To do this, I have needed older Joomla 1.6 / 1.7upgrade package files - the package files for old releases are very hard to find.
Here is what I did:
- Found a link to use to upgrade to Joomla 1.6.6 from an earlier version of Joomla 1.6 - http://joomlacode.org/gf/project/joomla/frs/?action=FrsReleaseBrowse&frs_package_id=6007
This was a very hard link to find!
- From there I was able to update from 1.6.6 to 1.7 using the manual process here (hard work!) http://docs.joomla.org/Upgrading_1.6.5_to_1.7
- Then I upgraded from 1.7.0 to 1.7.5 using this package: http://joomlacode.org/gf/project/joomla/frs/?action=FrsReleaseBrowse&frs_package_id=6259
- Now using Joomla's automatic built in updater, it seems to work well to upgrade from 1.7.5 to 2.5.6. However, if you have problem with this, then from 1.7.5 you can upgrade to 2.5.1 using the package available here: http://joomlacode.org/gf/project/joomla/frs/?action=FrsReleaseBrowse&frs_package_id=6257. Finally you should be able to upgrade from 2.5.1 to the latest version using the automatic upgrader in Joomla.
Hope this helps everyone!