Fatal error: Cannot redeclare activate_plugin

WordPress 2.5 has recently been released. It is a major update to previous releases, and I must say it has a nice feel to it. But I nearly didn’t get to enjoy it….

I realise how important it is to backup your wordpress install (and database) should an upgrade not work.

Here’s what happened:

I upgraded via fantastico, and for the last few updates, I haven’t bothered backing up my data etc because I’ve never had problems.
When I loaded up my site, yeah it looked fine. But when I tried to go to my admin panel, a message (shown below) came up:

Fatal error: Cannot redeclare activate_plugin() (previously declared in /home/username/public_html/wp-content/plugins/installer/includes/functions.inc.php:69) in /home/username/public_html/wp-admin/includes/plugin.php on line 116

What the? After asking my friend Google what he problem was, it appears to be the ‘installer’ plugin that was causing the issue. I FTP’ed into my plugins and renamed the installer folder – which in effect made it treated like a new plugin (by WordPress), and thus deactivated. I was then able to get into my admin panel and carry on as normal.

The moral? Keep regular backups of your WordPress installation and SQL database, as well as deactivate all your plugins prior to upgrading.
Also, backups are fine, but have you ever tested doing a restore?
Another thing to keep in mind is that I decided to try and use the backup tar file that fantastico auto generates when updating. Guess what? the file was corrupt 🙁