Joomla 1.0 to 1.5

For anyone trying to upgrade JOOMLA 1.0 to 1.5, this cannot be done by simple click of button. Those are 2 different programs and must be upgraded through a multi-step process.

http://docs.joomla.org/Migrating_from_1.0.x_to_1.5_Stable

There is nothing we can do about this inconvenience, because we do not develop Joomla. Joomla decided it would be this way.