Did you try the 'refresh dependencies' option in the Grails menu (accesible if you right click on your project)?
Just running the "grails refresh-dependencies" command itself isn't sufficient to let the IDE pick up on dependency changes. You have to make the IDE itself 'refresh' its dependencies.
This is because The IDE and the command line tooling use seperate infrastructure for compiling your code. The IDE menu 'refresh dependencies' is supposed to synch-up both worlds with eachother. Typically you have to do this if you made changes to the project dependencies by editing your project's config files.
Kris De Volder -- SpringSource