I use Aptana Studio to program in Ruby on Rails.  Today, I upgraded Rails to 2.2.2 on my laptop and after I did that, Aptana complained that MySQL's driver had been removed.  The error happened after I loaded Mongrel inside Aptana and I tried to view the application's homepage.

This is the error that I'd get:

"!!! The bundled mysql.rb driver has been removed from Rails 2.2. Please install the mysql gem and try again: gem install mysql."

After reinstalling everything a few times, I found a forum post that put me on the right direction.

When I upgraded, it installed a newer version of the MySQL gem, which apparently doesn't work well with Aptana.  To fix, I put the old MySQL dll in my ruby\bin folder, and it worked like a champ.

The dll file is here:

http://instantrails.rubyforge.org/svn/trunk/InstantRails-win/InstantRails/mysql/bin/libmySQL.dll

I'm using the InstantRails package, and so my ruby folder is here: c:\rails\ruby\bin

I then restarted the MySQL server and Aptana and it worked perfectly.