problem upgrading from 1.2 to latest

i have a blog at WzJz.net and it is wordpress 1.2. It is very old and now I am having trouble upgrading. I did not have the time to upgrade in the past and Now it won’t even let me log into my admin panel – says “database is outdated please upgrade”

when I go to upgrade to 1.5 as I should before upgrading to 2.3 – i get this error: Fatal error: Cannot access empty property in /home/username/public_html/wordpress/wp-admin/upgrade-functions.php on line 292

help on this issue is appreciated as I have to update my blog as well as upgrade it.

thanks!