Very frustrating day.
Followed the Upgrade.txt steps, but when finally at step 13, visit upgrade.php, I got the error message:
“Drupal 7 requires PHP 5.2.4 or higher with the PHP Data Objects (PDO) extension enabled.”
Round and round. Checked the host site to make sure php and PDO were there. php -i reported php 5.2.13 and PDO extensions for mysql working. Googled all over but got nothing but dead ends. Changed the connection info to look like D7 settings.php, but that did nothing.
Finally, copied program files back from backup, but the site wouldn’t go anyplace but the home page — got internal server error whenever navigated to an interior page.
Emptied all tables and dropped them, restored database to yesterday’s version, copied all the drupal-6.20 files on top of installation. Voila! It’s back to a nice 6.20 install.
Good to have backups.