> It doesn't work :-(  The error message doesn't make sense to me, so
> I'm hoping someone can enlighten me.  Maybe I'm not using the
> libraries correctly.  Thanks for the help.

There's a good explanation here:

http://stuff-things.net/2007/06/11/encrypting-sensitive-data-with-ruby-on-rails/

The last paragraph is what you're looking for.

Basically, you can only encrypt a message with length up to your key size in bytes
(128) - 11 for padding, which is 117 bytes.  Depending on your total message size,
you'll have to either use a bigger key (which will make the encrypt/decrypt slower)
or use a different encryption/decryption model.

Caleb