Error while running cron.php before upgrading to drupal 6

Ok, so I'm a bit nervous doing my first drupal upgrade on a live site. I followed the instructions on the upgrade screencast, as I detail below, and now i'm getting a series of errors as i try to run update.php.

1- I backed up both the database and all the files in the public_html folder.
2- Upgraded all of my current modules as per the upgrade status module. After that, I uninstalled the module.
3- I went to run update.php, but i got a white screen every time. As i read on the forums, this might be caused by a memory problem, so I unchecked all of my modules except for Views and CCK.
4- Still no luck running update.php so I erased all of the contributed modules (except for CCK and Views) from the sites/all/modules folder. I figured as i have them backed up, and i'm replacing them for their drupal 6 version, there would be no problem.
5- I changed my theme to bluemarine and tried to run update.php again and this time it worked, giving me the option to run the database upgrade script.
6- Now when i run the script, i get the problem: Fatal error: Unsupported operand types in .../includes/form.inc on line 342 . There is no way I can successfully run the script. Then i go to my modules directory, and i get the error
Fatal error: Call to undefined function user_access() in .../sites/all/modules/cck/content.module on line 88 . Even if i delete cck and views from my modules directory, i get the first error in any admin page.

I havent seen anything that matches what i'm describing on the forums, and I'm new at this, so I'm beginning to freak out. Any help would be appreciated.