I think you need to install the Groovy Eclipse support. I think the error shows that the Grails tools are not able to find the Groovy Eclipse components that they require.
You can install Groovy Eclipse from the extensions page.
This is the telling bit of the error message:
126.96.36.199203221000-RELEASE) requires 'bundle org.codehaus.groovy.eclipse.core 0.0.0' but it could not be found
(Yes those errors can be rather confusing, a lot of garbage text and a bit of guess work needed to figure out which part of this text is the actual problem :-)
Kris De Volder -- SpringSource